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Civil Aviation Development & Discussion

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chetak
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Re: Civil Aviation Development & Discussion

Postby chetak » 07 Jan 2018 21:29

rsingh wrote:
Mort Walker wrote:

And to the pilots for not making an error! Really bad errors like Charkhi-Dadri mid air collision in 1996 caused by the Kazak pilot not following ATC instructions are always in the back of the mind.


One has to question. why Mumbai has only one runway? What were they thinking when it was planned? Even modern airport in India has one runway. Most stupid thing.


vote bank slum dwellers = forceful occupation of land = rent collecting goondas = politicians + cops = single runway

That's why Bombay has one runway.

chetak
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Re: Civil Aviation Development & Discussion

Postby chetak » 07 Jan 2018 21:34

JayS wrote:Re Pusher config in Saras, the discussion that was going on in RnD thread. I think folks are hyperventilating over a non-issue. Rear mounted engines make a lot of sense for smaller aircraft like Saras. From there to pusher config is only a small step. Any config chosen would have pros and cons anyway and cons would need to be dealt with. Only designers would know all trade offs made.

As such its in NAL's DNA to go for TFTA solutions. Its a premier Aerospace "Lab" of India. They know they can deal with it. If one wanted proper commercial project out of Saras, NAL was a wrong choice for it always. To their credit, at least they dreamt of building an aircraft like Saras all by themselves without much background (and developed some awesome technology in composite wing making for example) when no one would touch it by even a mile long pole. And its not like GOI has flooded the project with funds. They have been running on fumes.


read the saras accident report.

The very same one where three IAF people died senselessly because of configuration management issues.

locals shot phone videos of the three injured crew alive and burning in the wreckage

someone should have been jailed at this premier Aerospace "Lab" of India, as you call it.

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Re: Civil Aviation Development & Discussion

Postby Indranil » 07 Jan 2018 23:23

Sir,

Did you read that report? I read it front to back, multiple times. There was lacuna on behalf of NAL and ASTE about following flight testing procedures, but no design fault was found.

The test was to switch off both engines and relight. After turning off the engines, the pilots did not feather the propeller and followed incorrect light up sequence. Consequently, the propellers kept windmilling increasingly drag immensely. It is like dragging a disk through air. This led to very low glide ratio and eventual departure.

The reason for this pilot-error was attributed to the change of engine and its relight sequence. I can’t understand where is the design flaw. Also, why should NAL scientist be hanged because locals were taking pictures/videos?

As Jay said, pusher props are not any more technologically challenging than tractors. And as Karan said NAL went down this path because of the initial tie up with the Russian design agency.

Flight testing and crashing go hand in hand. Indian flight testing has been relatively event free.

chetak
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Re: Civil Aviation Development & Discussion

Postby chetak » 07 Jan 2018 23:54

Indranil wrote:Sir,

Did you read that report? I read it front to back, multiple times. There was lacuna on behalf of NAL and ASTE about following flight testing procedures, but no design fault was found.

The test was to switch off both engines and relight. After turning off the engines, the pilots did not feather the propeller and followed incorrect light up sequence. Consequently, the propellers kept windmilling increasingly drag immensely. It is like dragging a disk through air. This led to very low glide ratio and eventual departure.

The reason for this pilot-error was attributed to the change of engine and its relight sequence. I can’t understand where is the design flaw. Also, why should NAL scientist be hanged because locals were taking pictures/videos?

As Jay said, pusher props are not any more technologically challenging than tractors. And as Karan said NAL went down this path because of the initial tie up with the Russian design agency.

Flight testing and crashing go hand in hand. Indian flight testing has been relatively event free.


Sirji,

I would not have commented without reading the report, multiple times, as you say.

Where did I say "design fault"??

IIRC, there was, however, some rumbling of some reports of the tail not having enough authority per some european consultant who was asked to review.

I specifically said configuration management issues which were directly responsible for the fatalities.

A full fledged configuration audit is both mandatory and inescapable before release of any aircraft for tests. If only it had been done, the fatal mistake of not providing updated and correct in-flight shutdown and relight procedures would not have happened. The previous documentation should have been destroyed and a record of its destruction should have been produced during the audit. This was not done. The holes in the swiss cheese are beginning to line up now.

Families were destroyed because some ignorant dolt did not do his job and some idiot supervisor did not bother to check and someone did not audit the processes properly.

In my book, all three should have been sacked as well as jailed. What about the bereaved families??

so the design was outsourced, the flight testing was outsourced, who really was the owner of the project ?? Anyone?? someone?? or no one??

There was TOTAL lack of leadership as well as ownership all around.

the pilots did not feather the propeller and followed incorrect light up sequence.

The holes in the swiss cheese have completely lined up now. The fatality is only minutes away and it is unstoppable.



The ASTE crew followed precisely the procedures given to them in writing by NAL.

and these procedures were WRONG and it was these wrong procedures that killed them.

So the engines were changed but the documentation was not??

such outstanding leadership/ownership at this premier Aerospace "Lab" of India??

and finally, pilot error?? really??

That is really one "politically correct" investigation report, no??

I could never be so casual about flight testing and crashing going hand in hand. The first time after one picks pieces of crew from any crash site, all casualness just vanishes forever and that's true for most people. Sorry for the crude language.

old jungle saying:

if pilot dead, it is pilot error.

If pilot not dead, it is a material failure.

shiv
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Re: Civil Aviation Development & Discussion

Postby shiv » 08 Jan 2018 06:57

JayS wrote:Re Pusher config in Saras, the discussion that was going on in RnD thread. I think folks are hyperventilating over a non-issue. Rear mounted engines make a lot of sense for smaller aircraft like Saras. From there to pusher config is only a small step. Any config chosen would have pros and cons anyway and cons would need to be dealt with. Only designers would know all trade offs made.

As such its in NAL's DNA to go for TFTA solutions. Its a premier Aerospace "Lab" of India. They know they can deal with it. If one wanted proper commercial project out of Saras, NAL was a wrong choice for it always. To their credit, at least they dreamt of building an aircraft like Saras all by themselves without much background (and developed some awesome technology in composite wing making for example) when no one would touch it by even a mile long pole. And its not like GOI has flooded the project with funds. They have been running on fumes.

Apart from clean wings the pusher configuration will have a much smaller tendency to yaw and therefore more easily controllable in case of single engine failure. Cabin noise is an added bonus but not critical.

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Re: Civil Aviation Development & Discussion

Postby chola » 08 Jan 2018 07:39

^^^ Really?

Also why the extreme disproportionate ratio of tractors to pushers unless there are major disadvantages? I can’t think of one turboprop pusher outside the Saras to be perfectly honest.

https://aviation.stackexchange.com/questions/3306/why-are-push-propellers-so-rare-yet-they-are-still-around
There are many disadvantages, they seem to outweigh the advantages.

Here are two:

A pusher prop is working in a disturbed airflow, causing increased vibration and noise
If the propeller is fitted behind a wing, each propeller blade is passing through the separated boundary flow twice each rotation. These cycles create additional noise and lower the efficiency of the propeller. The vibration makes the propeller blades more susceptible to metal fatigue.
Propeller clearance at takeoff
Due to the pitch up at take-off, the propeller gets close to the ground. Therefore the diameter needs to be reduced (loss of efficiency) or the landing gear struts need to be made longer (added weight). Since the propeller is behind the landing gear, it is susceptible to debris kicked up from the gear, increasing the need for added blade protection (increased weight, loss of efficiency)

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Re: Civil Aviation Development & Discussion

Postby shiv » 08 Jan 2018 08:09

chola wrote:
Also why the extreme disproportionate ratio of tractors to pushers unless there are major disadvantages? I can’t think of one turboprop pusher outside the Saras to be perfectly honest.

https://aviation.stackexchange.com/questions/3306/why-are-push-propellers-so-rare-yet-they-are-still-around
There are many disadvantages, they seem to outweigh the advantages.



Design experience is one reason for staying with pushers rather than tractors like the Dassault and Cessna jets.

As regards props I cannot think of a more silly and hilarious excuse than "prop will hit the floor on take off". Any damfool designer will place props high enough to prevent that.

The other urgent Google search you have linked says this - in case you missed it first time. And after reading it look at an image of the Saras and tell me which wing disturbs the engine airflow.
A pusher prop is working in a disturbed airflow, causing increased vibration and noise
If the propeller is fitted behind a wing, each propeller blade is passing through the separated boundary flow twice each rotation. These cycles create additional noise and lower the efficiency of the propeller. The vibration makes the propeller blades more susceptible to metal fatigue.


https://www.youtube.com/watch?v=yqt30aI3Zzw



Piaggio Avanti
Image

Nobody is worrying about :D "disturbed airflow" here
Image

No one seems to be concerned about "propeller hitting floor" here
Image

"Disturbed airflow "anyone? :D
Image

South African COIN aircraft
Image

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Re: Civil Aviation Development & Discussion

Postby chola » 08 Jan 2018 08:47

^^^ Acknowledged that there are pushers and people had engineered around the disadvantages.

There is the disproportionate number of tractors over pushers that cannot be explained by just having previous experience with tractors. Everyone was more experienced with straight wings after WWII yet they all went to swept wings after.

Here is more, answered by a couple of aeronautic engineers: https://www.quora.com/What-advantage-does-a-push-propeller-have-compared-to-a-pull-tractor-propeller-on-a-plane:

That all being said, there are disadvantages as well, hence we don’t see that many pushers flying in the sky. The wing gets a clear flow, but the propeller itself is in a wake now, decreasing its efficiency. Ground clearance is very important (I disregarded it in one of my aeromodelling design courses and broke the propeller on the runway, almost failing that course!)

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Re: Civil Aviation Development & Discussion

Postby shiv » 08 Jan 2018 08:58

chola wrote:There is the disproportionate number of tractors over pushers that cannot be explained by just having previous experience with tractors. Everyone was more experienced with straight wings after WWII yet they all went to swept wings after.

When a man lies with a woman for the first time what he does cannot be dictated by what most other people do. He may choose Malabar shot rather than missionary position and still be effective. The fact that more people do different things is not sufficient proof that a particular method is wrong.

The straight and swept wing example is irrelevant. Early jet aircraft had straight wings. Swept wings were adopted only to reduce drag to enable the far higher speeds and thrust that jet engines provide. Aircraft design is not fashion. It is done with a plan. If you have a quibble with the plan - please say why. Claiming that X did this so Y is wrong is gossip not gyan

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Re: Civil Aviation Development & Discussion

Postby chola » 08 Jan 2018 09:08

In any eco-system, certain configurations becomes the norm because of advantages — for example, even manmals like whales and porpoises are mistaken for fish because the planform they evolved to converged with that of fish.

There is a reason why tractors are so ubiquitous among turboprops and I assume it is because of market/evolutionary advantages.

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Re: Civil Aviation Development & Discussion

Postby SriKumar » 08 Jan 2018 09:24

The report mentioned control problems (and described it in detail). Does anyone know what was the source of the aircraft control issue with one engine running? The report gives a long list of the issues faced-with a lot of specifics, and one assumes that most or all of these were acted upon and changes made to configuration. A Hindu article (Sep 2017) mentions 10 modifications were done to 'improve pilot control' and 'agility'. There is no specifics as to what was modified.

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Re: Civil Aviation Development & Discussion

Postby shiv » 08 Jan 2018 10:04

SriKumar wrote:The report mentioned control problems (and described it in detail). Does anyone know what was the source of the aircraft control issue with one engine running? The report gives a long list of the issues faced-with a lot of specifics, and one assumes that most or all of these were acted upon and changes made to configuration. A Hindu article (Sep 2017) mentions 10 modifications were done to 'improve pilot control' and 'agility'. There is no specifics as to what was modified.

If I remember right - it was supposed to be a test of shutting down one engine and there was a serious error in the procedure for doing that led to the accident. My memory of detail is vague - the report is out there somewhere but I think it was something like this:

Shutting down one engine obviously causes asymmetric thrust leading to yawing, so the procedure for shutting down included feathering the prop of the engine to be shut down. IIIRC what actually happened was that the blades were not feathered fully due to a procedural issue with that engine-prop combination so the shut down engine actually acted like a sail while the other engine continued to provide thrust leading to loss of control. This detail may be all wrong so please don't take it as the last word. I will try and locate the original report.

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Re: Civil Aviation Development & Discussion

Postby SriKumar » 08 Jan 2018 11:02

Its online and I went through it recently.....a LOT of detail. And there are several reasons/factors given- about 5 to 10 (certainly more than 2 or 3). The Conclusions section lists them all, plus some other problematic issues not contributing to the cause of the final event. One thing that was not clearly described was the cause/reason for sudden and significant loss of altitude (not yawing) after shut-down of one engine. They speculate about a downward force. And there was something about 'side-slipping' by 22 degrees. In any case, the sudden loss of altitude severely reduced the time for recovery. I am not sure what has been modified in the latest configuration to address this point. Certainly, there is clarity now about the feathering aspect.
Last edited by SriKumar on 08 Jan 2018 11:07, edited 1 time in total.

Indranil
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Re: Civil Aviation Development & Discussion

Postby Indranil » 08 Jan 2018 11:06

Chetak sir,

I understand your emotions and share it. But discussing this is below us. Essentially, you and me are sitting on the fence and passing sanctimonious comments over the dead bodies of three young men about whose fault was it. The men who died and the men whose heads you now ask for were friends who worked together on a daily basis. You are suggesting that the latter did not care for the formers' lives enough?

I don't intend to pin the fault on anybody. I said pilot error because the report said so. Indeed, there were many slip ups by various parties within ASTE/NAL/CEMILAC/DGCA and even the pilots. Did NAL cause the accident? Here's why I say no.

1. You say that NAL did not provide the right documentation for relight. This is factually wrong. There were no old documents to be destroyed and no new documents to be provided. NAL did not suspect that it could be a propeller problem. They contacted P&W about relight prior to the test. P&W said that the engine can restart in any propeller setting. Feathering was at pilot's discretion. NAL didn't realize that there was a quirk left. So, although they were in constant contact with MT (propeller OEM), they did not inquire about this and MT did not tell them anything. The outcome of this series of human error was one lever in the wrong position, at the wrong time. The accident report pins this as the only error on the management part which led to the accident: inability to provide clear relight procedure.

2. Saras is the first civilian aircraft that India is flight testing and certifying. ASTE/Cemilac/NAL/DGCA/pilots: everybody is learning on the job. The PD (from NAL) was understandably risk averse and categorically briefed the pilots to return if the first relight attempt failed.
It has been observed from the records and statements th at pre-flight briefing meeting was done in the afternoon of 6.3.2009 prior to the test flight 49 in which NAL and ASTE took part of it . This meeting covered SOP for the flight, aircraft serviceability, configuration limits, test points, and test sequenc e etc as per the test program. Flight crew were also present. It is also understood that at the end of the briefing the pilots were specifically told by FTD that in case of any problem during the relight attempt, the engine should be switched off, propeller feathered and single engine landing executed. No effort should be made to try the relight at second time. This was also repeated to them orally near the aircraft before the crew got into the aircraft.

The Control tower inquired at the first signs of trouble (mismatch of telemetry altitude and pilots readout). The flight test engineer asked the pilots to abort testing and return. He was hilariously replied, "there is a road for the emergency".
Crew were also not responding to the doubts raised by FTD on three occasions even at one stage after the initiation of first relighting at about 37 secs prior to crash. FTD also failed to call for the aborting off flight after the abnormal telemetry link as well as abnormal flight situation including rapid loss of predetermined height and not getting response from the pilot at critical stages.

Similarly ASTE supervisor also failed in his responsibilities for flight safety in co -ordination with FTD as the situation warranted. It is also informed that alongwith FTD Wg Cdr Jaiswal,Test pilot -Saras,Wg Cdr G.D.singh, FTE_Saras were also monitoring the flight at Telemetry. They also failed to advise FTD for calling off the flight seeing the abnormal situation in the monitor.

Therefore, to ask for the heads of NAL's employees only is grossly unfair

3. Inadequate rudder authority is also misrepresented on many reports. Saras's rudder is in accordance to the FAR-23 standards. But for the purposes of the testing (like the one above), it was at the limit which is what the accident report highlighted. PT1N has a larger rudder. NAL also adopted many other recommendations of the accident report as well. But none of them are design flaws!

4. The accident report outlines many missed documentations on NAL's behalf. But none of them are reasons for the crash.

chetak
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Re: Civil Aviation Development & Discussion

Postby chetak » 08 Jan 2018 11:07

shiv wrote:
JayS wrote:Re Pusher config in Saras, the discussion that was going on in RnD thread. I think folks are hyperventilating over a non-issue. Rear mounted engines make a lot of sense for smaller aircraft like Saras. From there to pusher config is only a small step. Any config chosen would have pros and cons anyway and cons would need to be dealt with. Only designers would know all trade offs made.

As such its in NAL's DNA to go for TFTA solutions. Its a premier Aerospace "Lab" of India. They know they can deal with it. If one wanted proper commercial project out of Saras, NAL was a wrong choice for it always. To their credit, at least they dreamt of building an aircraft like Saras all by themselves without much background (and developed some awesome technology in composite wing making for example) when no one would touch it by even a mile long pole. And its not like GOI has flooded the project with funds. They have been running on fumes.

Apart from clean wings the pusher configuration will have a much smaller tendency to yaw and therefore more easily controllable in case of single engine failure. Cabin noise is an added bonus but not critical.


Word for word, the above is also identically true for a tractor configuration with similar tail mounted engines.

The Boeing 727, for instance, no??

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Re: Civil Aviation Development & Discussion

Postby Indranil » 08 Jan 2018 11:23

Now, I want to return to some technical discussions. For the people saying that Saras is more prone to FOD damage than a high wing pusher.

Imagine an aircraft with a high wing. Would the engines have been any higher?
Image

At what angle of attack would the propeller touch the ground?
Image

Would other parts of the fuselage touch the runway before the propellers?
Image

I have problem with Saras as a commuter. Is a separate luggage loading door even possible? Ability to use the space behind the rear pressure bulkhead would have been awesome, but most likely improbable.

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Re: Civil Aviation Development & Discussion

Postby chetak » 08 Jan 2018 11:42

Indranil wrote:Chetak sir,

I understand your emotions and share it. But discussing this is below us. Essentially, you and me are sitting on the fence and passing sanctimonious comments over the dead bodies of three young men about whose fault was it. The men who died and the men whose heads you now ask for were friends who worked together on a daily basis. You are suggesting that the latter did not care for the formers' lives enough?

I don't intend to pin the fault on anybody. I said pilot error because the report said so. Indeed, there were many slip ups by various parties within ASTE/NAL/CEMILAC/DGCA and even the pilots. Did NAL cause the accident? Here's why I say no.

1. You say that NAL did not provide the right documentation for relight. This is factually wrong. There were no old documents to be destroyed and no new documents to be provided. NAL did not suspect that it could be a propeller problem. They contacted P&W about relight prior to the test. P&W said that the engine can restart in any propeller setting. Feathering was at pilot's discretion. NAL didn't realize that there was a quirk left. So, although they were in constant contact with MT (propeller OEM), they did not inquire about this and MT did not tell them anything. The outcome of this series of human error was one lever in the wrong position, at the wrong time. The accident report pins this as the only error on the management part which led to the accident: inability to provide clear relight procedure.

2. Saras is the first civilian aircraft that India is flight testing and certifying. ASTE/Cemilac/NAL/DGCA/pilots: everybody is learning on the job. The PD (from NAL) was understandably risk averse and categorically briefed the pilots to return if the first relight attempt failed.
It has been observed from the records and statements th at pre-flight briefing meeting was done in the afternoon of 6.3.2009 prior to the test flight 49 in which NAL and ASTE took part of it . This meeting covered SOP for the flight, aircraft serviceability, configuration limits, test points, and test sequenc e etc as per the test program. Flight crew were also present. It is also understood that at the end of the briefing the pilots were specifically told by FTD that in case of any problem during the relight attempt, the engine should be switched off, propeller feathered and single engine landing executed. No effort should be made to try the relight at second time. This was also repeated to them orally near the aircraft before the crew got into the aircraft.

The Control tower inquired at the first signs of trouble (mismatch of telemetry altitude and pilots readout). The flight test engineer asked the pilots to abort testing and return. He was hilariously replied, "there is a road for the emergency".
Crew were also not responding to the doubts raised by FTD on three occasions even at one stage after the initiation of first relighting at about 37 secs prior to crash. FTD also failed to call for the aborting off flight after the abnormal telemetry link as well as abnormal flight situation including rapid loss of predetermined height and not getting response from the pilot at critical stages.

Similarly ASTE supervisor also failed in his responsibilities for flight safety in co -ordination with FTD as the situation warranted. It is also informed that alongwith FTD Wg Cdr Jaiswal,Test pilot -Saras,Wg Cdr G.D.singh, FTE_Saras were also monitoring the flight at Telemetry. They also failed to advise FTD for calling off the flight seeing the abnormal situation in the monitor.

Therefore, to ask for the heads of NAL's employees only is grossly unfair

3. Inadequate rudder authority is also misrepresented on many reports. Saras's rudder is in accordance to the FAR-23 standards. But for the purposes of the testing (like the one above), it was at the limit which is what the accident report highlighted. PT1N has a larger rudder. NAL also adopted many other recommendations of the accident report as well. But none of them are design flaws!

4. The accident report outlines many missed documentations on NAL's behalf. But none of them are reasons for the crash.


Indranil ji,

I wish that I could reply without compromising sources on an open forum and also keep in mind that baboo(n)s and reports are very compatible bedfellows.

My take is very different from yours. Pilot error, it most certainly was not.

If it were up to me, I would have taken the heads without a second thought.

Talk about holes in the swiss cheese lining up. This is a classic case.

BTW, a new and more powerful engine, larger props, significantly higher torque and yet the basic question of rudder authority was never seriously investigated and now, voila, the rudder has miraculously become larger??

and yes, even after all these years, dead crew upsets me, wherever, whenever and however.

Just making things "idiot proof" and then sitting back is never the answer, eternal vigil is, because most unexpectedly, and in a black swan kind of way, a new and improved idiot always pops up.

Incidentally, most of the things in the report should have been discovered and corrected by NAL in any mundane audit. Like I said, leadership and ownership.

Finally, in any long gestation project, especially an ab initio aviation project, it would do well to remember the eternal truth:

The only difference between a rut and a grave is the depth.

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Re: Civil Aviation Development & Discussion

Postby Indranil » 08 Jan 2018 12:16

This is getting a little bizzare. You are claiming that DGCA is conspiring with NAL to pass the buck on the pilots. ASTE is silent. And all this in the presence of telemetry and FDR data. And there is a public report scrutinizing every second of the data.

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Re: Civil Aviation Development & Discussion

Postby chetak » 08 Jan 2018 12:20

SriKumar wrote:Its online and I went through it recently.....a LOT of detail. And there are several reasons/factors given- about 5 to 10 (certainly more than 2 or 3). The Conclusions section lists them all, plus some other problematic issues not contributing to the cause of the final event. One thing that was not clearly described was the cause/reason for sudden and significant loss of altitude (not yawing) after shut-down of one engine. They speculate about a downward force. And there was something about 'side-slipping' by 22 degrees. In any case, the sudden loss of altitude severely reduced the time for recovery. I am not sure what has been modified in the latest configuration to address this point. Certainly, there is clarity now about the feathering aspect.


Memory is now vague and IIRC, they entered single engine at approx 8000 odd ft instead of the briefed 10,000 ft. This needs corroboration.

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Re: Civil Aviation Development & Discussion

Postby Indranil » 08 Jan 2018 12:24

They entered at 10, lost altitude very quickly and leveled out at 8. They started first relight attempt there.

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Re: Civil Aviation Development & Discussion

Postby shiv » 08 Jan 2018 12:25

chetak wrote:
shiv wrote:Apart from clean wings the pusher configuration will have a much smaller tendency to yaw and therefore more easily controllable in case of single engine failure. Cabin noise is an added bonus but not critical.


Word for word, the above is also identically true for a tractor configuration with similar tail mounted engines.

The Boeing 727, for instance, no??


Jet is a different issue. For a short haul feederliner prop is a good choice.

Once you decide on clean wings the engines must go on fuselage sides (if your design is not single engine). The only practical available space is the rear fuselage. The choice for prop has to be between puller prop which will stick out in front, or pusher sticking out at back. Of these pusher is better because access to doors and cargo hatches on fuselage sides will be blocked by a puller prop but not by pusher.

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Re: Civil Aviation Development & Discussion

Postby chola » 08 Jan 2018 12:31

I couldn’t help noticing that the pushers that Shiv posted all look like Sci-Fi devices — except the Saras. They also have canards — except the Saras

So I, at risk of sounding like an idiot, did more trusty googling.

https://en.m.wikipedia.org/wiki/Pusher_configuration

A pusher design with an empennage behind the propeller is structurally more complex than a similar tractor type. The increased weight and drag degrades performance compared with a similar tractor type. Modern aerodynamic knowledge and construction methods may reduce but never eliminate the difference.

...

Due to a generally high thrust line (needed for propeller ground clearance), negative (down) pitching moment and sometimes absence of prop-wash over the tail, higher speed and longer roll is required for takeoff compared to tractor aircraft.

...

Due to the generally high thrust line (aft propeller/ ground clearance), a low wing pusher layout may suffer pitch changes with power variation (pitch/power coupling).

...

The propeller passes through the fuselage wake, wing and other flight surface downwashes - moving asymmetrically through a disk of irregular airspeed. This reduces propeller efficiency and causes vibration inducing structural propeller fatigue and noise.

...

Prop efficiency is usually at least 2-5 % less and in some cases more than 15% less than an equivalent tractor installation. Fullscale wind tunnel investigation of the canard Rutan VariEze showed a propeller efficiency of 0.75 compared to 0.85 for a tractor configuration - a loss of 12%.



Now, the disadvantages listed above have nothing to do with the accident.

But they do indicate that NAL perhaps chose a harder design than necessary for their first project? The configuration’s affect on the propeller’s efficiency along with the weight penalty imposed by it cut down on the margin of error.

Less power, more weight, not to mention pitch issues mean the designer must work harder to overcome those inherent issues? Again, the above examples of the other pushers are engineered like fighter jets (complete with canards.) The Saras look decidedly conventional save for the location of the props.

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Re: Civil Aviation Development & Discussion

Postby Zynda » 08 Jan 2018 12:32

JayS wrote:.

Saar...sent you an email at ABC. Please reply when you get a chance. Thx...

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Re: Civil Aviation Development & Discussion

Postby chetak » 08 Jan 2018 12:46

shiv wrote:
chetak wrote:
Word for word, the above is also identically true for a tractor configuration with similar tail mounted engines.

The Boeing 727, for instance, no??


Jet is a different issue. For a short haul feederliner prop is a good choice.

Once you decide on clean wings the engines must go on fuselage sides (if your design is not single engine). The only practical available space is the rear fuselage. The choice for prop has to be between puller prop which will stick out in front, or pusher sticking out at back. Of these pusher is better because access to doors and cargo hatches on fuselage sides will be blocked by a puller prop but not by pusher.


not talking economics of turboprops/shorthaul but from the point of cabin noise and yaw dynamics due engine loss onlee.

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Re: Civil Aviation Development & Discussion

Postby nachiket » 08 Jan 2018 13:02

Indranil wrote:Sir,

Did you read that report? I read it front to back, multiple times. There was lacuna on behalf of NAL and ASTE about following flight testing procedures, but no design fault was found.

The test was to switch off both engines and relight. After turning off the engines, the pilots did not feather the propeller and followed incorrect light up sequence. Consequently, the propellers kept windmilling increasingly drag immensely. It is like dragging a disk through air. This led to very low glide ratio and eventual departure.

The reason for this pilot-error was attributed to the change of engine and its relight sequence. I can’t understand where is the design flaw. Also, why should NAL scientist be hanged because locals were taking pictures/videos?

Indranil guru, a small question here. Don't turboprops have an auto-feather system which detects loss of torque from the engine and automatically feathers the propeller? Does this system still work if the engine is manually shut off in flight as it would be during this test scenario here?

Of course even this is not error or pilot proof. In a recent ATR crash in Taiwan a few years ago, the auto-feather system developed some fault immediately after takeoff and feathered the propeller of a perfectly fine engine. Thereafter, the pilot got confused and went ahead and shut off the wrong engine. The aircraft was unrecoverable after that.

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Re: Civil Aviation Development & Discussion

Postby Indranil » 08 Jan 2018 13:05

chola wrote:
A pusher design with an empennage behind the propeller is structurally more complex than a similar tractor type. The increased weight and drag degrades performance compared with a similar tractor type. Modern aerodynamic knowledge and construction methods may reduce but never eliminate the difference.

...

Due to a generally high thrust line (needed for propeller ground clearance), negative (down) pitching moment and sometimes absence of prop-wash over the tail, higher speed and longer roll is required for takeoff compared to tractor aircraft.

...

Due to the generally high thrust line (aft propeller/ ground clearance), a low wing pusher layout may suffer pitch changes with power variation (pitch/power coupling).

...

The propeller passes through the fuselage wake, wing and other flight surface downwashes - moving asymmetrically through a disk of irregular airspeed. This reduces propeller efficiency and causes vibration inducing structural propeller fatigue and noise.

...

Prop efficiency is usually at least 2-5 % less and in some cases more than 15% less than an equivalent tractor installation. Fullscale wind tunnel investigation of the canard Rutan VariEze showed a propeller efficiency of 0.75 compared to 0.85 for a tractor configuration - a loss of 12%.


Sir, which of these apply to the Saras config. Saras’s props don’t lie in either the fuselage wake or that of the wing.

Also, for non canard equivalent look up the Vector 123 and Duet Saras.

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Re: Civil Aviation Development & Discussion

Postby deejay » 08 Jan 2018 13:07

Indranil wrote:Chetak sir,

....

2. Saras is the first civilian aircraft that India is flight testing and certifying. ASTE/Cemilac/NAL/DGCA/pilots: everybody is learning on the job. The PD (from NAL) was understandably risk averse and categorically briefed the pilots to return if the first relight attempt failed.

...


Indranil, Chetak Sir - with due respect to you and your opinions - I would say irrespective of whom you blame, crashes cannot be ruled out in flying and specially in Test Flying. Pilot as the person in the cockpit will take the blame. Ethics, morals, departed souls, etc are for the inner community but for the public at large it was an airplane that failed where the pilot most probably messed up. We have to live with this. Accident investigation will result in pilot taking some blame even in clear cases of mechanical failure. There is always something that the pilot could have done differently.

Now coming to the specific part of Indranil's comment above (and selectively bolded by me) is the reason why they should have gone with a conventional high wing design with conventional pusher type props mounted on them. For a first time, it would have been easier for everyone to get data, to get advice, to compare with other agencies, etc.

The first moment of truth for the programme will be certification by DGCA and the second moment of truth will be the first sale. Repeating this second moment of truth over and over again in a small civilian market where orders will come piece meal will be a tough ask. As always, large outlays as aircraft acquisition tend to be risk averse. People may pay more for a known product than a new product. Not only is NAL trying out a more unconventional design it is risking market acceptance. In a market segment where the Saras places itself (between a King Air (200/300), Avanti P 180 / B 1900, Twin Otter) the story is clearly is clearly scripted towards conventional design.

It's good to challenge frontiers but is NAL equipped to handle so many at a time?

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Re: Civil Aviation Development & Discussion

Postby Indranil » 08 Jan 2018 13:12

Nachiket, no guru and ji please.

Many propellers have. This engine-prop combo doesn’t. In fact this engine and prop combo is unique. They started with the beech starship config, but the manufacturer had stopped manufacturing the prop. So they had to evaluate all available props. They found the current MT’s props gave the best efficiency with the engine. So, they went with it.

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Re: Civil Aviation Development & Discussion

Postby Indranil » 08 Jan 2018 13:18

Deejay,

My stand on pinning blame is the same as yours. Human error lead to crashes. Crashes lead to deaths. It is inevitable. We gain nothing with pinning blame.

I agree with you on the non conventional part leading to possible low acceptance. But, what is passed as technical complications here doesn’t even pass common sense tests. There are others too. It’s a luxurious pressurized aircraft. Is there a market for that?

Why did they go there. I don’t think NAL ever was given a proper mandate and funding. The lowest hanging fruit was to latch onto the Saras Duet collaboration program when it came along. The rest is history.

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Re: Civil Aviation Development & Discussion

Postby Indranil » 08 Jan 2018 13:23

The only silver lining would be if they can quickly come up with the 18 seater and an economy business jet version. Obviously going to a 30 seater jet aircraft is the next step. Basically, Embraer’s path.

But I don’t expect it from NAL/HAL combo. With Tata, there might have been an outside chance.

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Re: Civil Aviation Development & Discussion

Postby shiv » 08 Jan 2018 14:41

chola wrote:A pusher design with an empennage behind the propeller is structurally more complex than a similar tractor type. The increased weight and drag degrades performance compared with a similar tractor type. Modern aerodynamic knowledge and construction methods may reduce but never eliminate the difference.
Not Saras: here is an example of your quote
https://flyawaysimulation.com/media/ima ... 2-fsx1.jpg

chola wrote:Due to a generally high thrust line (needed for propeller ground clearance), negative (down) pitching moment and sometimes absence of prop-wash over the tail, higher speed and longer roll is required for takeoff compared to tractor aircraft.
...
Due to the generally high thrust line (aft propeller/ ground clearance), a low wing pusher layout may suffer pitch changes with power variation (pitch/power coupling).

chola wrote:The propeller passes through the fuselage wake, wing and other flight surface downwashes - moving asymmetrically through a disk of irregular airspeed. This reduces propeller efficiency and causes vibration inducing structural propeller fatigue and noise.
Not Saras. Here is an example of your quote:
https://i.ytimg.com/vi/GsJagEM6E6g/hqdefault.jpg

chola wrote:Prop efficiency is usually at least 2-5 % less and in some cases more than 15% less than an equivalent tractor installation. Fullscale wind tunnel investigation of the canard Rutan VariEze showed a propeller efficiency of 0.75 compared to 0.85 for a tractor configuration - a loss of 12%.
Again. Nothing to do with the design of Saras. If you think some images look like SciFi please Google for Burt Rutan Aircraft

In fact India's Rustom I is a variant of Rutan VariEze
https://www.youtube.com/watch?v=seGfyTp3n1s

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Re: Civil Aviation Development & Discussion

Postby chetak » 08 Jan 2018 16:56

deejay wrote:
Indranil wrote:Chetak sir,

....

2. Saras is the first civilian aircraft that India is flight testing and certifying. ASTE/Cemilac/NAL/DGCA/pilots: everybody is learning on the job. The PD (from NAL) was understandably risk averse and categorically briefed the pilots to return if the first relight attempt failed.

...


Indranil, Chetak Sir - with due respect to you and your opinions - I would say irrespective of whom you blame, crashes cannot be ruled out in flying and specially in Test Flying. Pilot as the person in the cockpit will take the blame. Ethics, morals, departed souls, etc are for the inner community but for the public at large it was an airplane that failed where the pilot most probably messed up. We have to live with this. Accident investigation will result in pilot taking some blame even in clear cases of mechanical failure. There is always something that the pilot could have done differently.

Now coming to the specific part of Indranil's comment above (and selectively bolded by me) is the reason why they should have gone with a conventional high wing design with conventional pusher type props mounted on them. For a first time, it would have been easier for everyone to get data, to get advice, to compare with other agencies, etc.

The first moment of truth for the programme will be certification by DGCA and the second moment of truth will be the first sale. Repeating this second moment of truth over and over again in a small civilian market where orders will come piece meal will be a tough ask. As always, large outlays as aircraft acquisition tend to be risk averse. People may pay more for a known product than a new product. Not only is NAL trying out a more unconventional design it is risking market acceptance. In a market segment where the Saras places itself (between a King Air (200/300), Avanti P 180 / B 1900, Twin Otter) the story is clearly is clearly scripted towards conventional design.

It's good to challenge frontiers but is NAL equipped to handle so many at a time?


@deejay ji

From the very moment they entered the single-engine condition, there was no turning back thereafter and from that moment onward it was all over barring the actual impact.

It was the prop that either wouldn't or couldn't be feathered as per the NAL given procedure.

It's not merely about being risk averse but more about being risk aware and the mitigation options arising from that awareness. Risk averse usually gets you nowhere whereas risk aware gets the job done especially when coupled with a proper mitigation plan or action.

Risk analysis and failure mode analysis are done for a very good reason. These analyses, when done before flight is often very enlightening and when done after flight is sometimes heartbreaking.

Vision, that was never 20/20 before an event suddenly becomes 20/20 after the event.

FAA accident reports are clear, exhaustive and consider everything including human factors. Unfortunately, DGCA has yet to reach any level of maturity as far as accident investigations are concerned and very often extraneous factors dominate. Frequently, while waiting at some PSU for an aircraft delivery, I would sometimes get lucky and get my hands on some FAA accident reports.

It's just not enough for any PD to simply say come back and such an attitude doesn't cut any ice nor is it realistic. It also means that there was very little awareness of failure modes and the consequences thereof.

and we are back to the pilot again. why is he being made to carry the can??

have we moved away from aerodynamics and into the realm of sociology??

If the test pilots failed to respond to calls, just imagine the grim situation in the cockpit.

and finally, how did anyone expect the pilots to relight inflight when this happened as below:

@Indranil wrote:

NAL did not suspect that it could be a propeller problem. They contacted P&W about relight prior to the test. P&W said that the engine can restart in any propeller setting. Feathering was at pilot's discretion. NAL didn't realize that there was a quirk left. So, although they were in constant contact with MT (propeller OEM), they did not inquire about this and MT did not tell them anything. The outcome of this series of human error was one lever in the wrong position, at the wrong time. The accident report pins this as the only error on the management part which led to the accident: inability to provide clear relight procedure.


The series of human errors lining up is what I said about the holes in the swiss cheese lining up to initiate the single point failure mode.

The outcome of this series of human error was one lever in the wrong position, at the wrong time. The accident report pins this as the only error on the management part which led to the accident: inability to provide clear relight procedure.


If this is the conclusion or even one of the conclusions of the investigation, I would not blame the pilots.

Undoubtedly, ONLY the pilots were at the receiving end of this fatal single point failure mode but what about all the others who initiated and caused it in the first place?? Why do they get a free pass??

So, people who didn't know better were talking to the engine and propeller OEMs, each missing out crucial/fatal points because they were not situationally aware of the engine and the propeller combination being another, very different ball game altogether and they both seemingly approached the problem in magnificent isolation.

[/quote]
Last edited by chetak on 08 Jan 2018 17:42, edited 1 time in total.

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Re: Civil Aviation Development & Discussion

Postby Indranil » 08 Jan 2018 17:37

Chetak Sir,

I hate to say this but your cognition of what really happened is not in accordance to what the report says.

There was no wrong NAL procedure. There was no procedure at all other than standard practice. They had asked P&W and P&W said that relight is possible from any prop position. Feathering was at pilot’s discretion. NAL had tried this several times in the teatbench and every time it worked. Then, NAL and the pilots tried the relight sequence from within the aircraft while on the ground and everything went well because there was no windmilling on ground. So they proceeded with the flight test.

Going by your standards all flight design teams (the world over) should be hanged.

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Re: Civil Aviation Development & Discussion

Postby chetak » 08 Jan 2018 18:26

Indranil wrote:Chetak Sir,

I hate to say this but your cognition of what really happened is not in accordance to what the report says.

There was no wrong NAL procedure. There was no procedure at all other than standard practice. They had asked P&W and P&W said that relight is possible from any prop position. Feathering was at pilot’s discretion. NAL had tried this several times in the teatbench and every time it worked. Then, NAL and the pilots tried the relight sequence from within the aircraft while on the ground and everything went well because there was no windmilling on ground. So they proceeded with the flight test.

Going by your standards all flight design teams (the world over) should be hanged.


Indranil ji,

Let's not discuss this any further.

Design teams are at fault a lot of the times and the pilots too are not free of this menace.

That's why design teams should follow a strict and detailed design process, for instance, the US DOD/NASA derived process which has been already well documented and detailed, now crystallized after being extensively refined using the inputs of countless failures, improvements and the subsequent verified corrective measures. Such design formats, in one form or the other are followed the world over. Risk and failure mode analysis form the heart of any design process.

Many organisations use the process as developed or derive a variation of the process to suit their particular use. In almost in all cases, the basic provisos remain untouched.

To make absurd statements like "accidents will happen and people will die" is to take a fatalistic view and such a view is certainly not acceptable in today's world. A view that is unsafe and unwarranted as part of a design mindset, per se.

It's a designers job to make sure that there are no accidents or even surprises and the pilot's job to take forward the designer's vision and flesh it out as it were. Risk and failure mode analysis form the heart of any design process and I cannot stress this enough. If done systematically, exhaustively and comprehensively, involving all stake holders including outsourced stakeholders, it all but eliminates accidents and surprises minus of course, acts of god.

If one of the designer's pet assumptions is that "accidents will happen and people will die", then such designers should man up and have the testimonials to accompany the test pilot for every test flight.

If it was a black swan event, it is understandable but this fatality was the result of a series of eminently avoidable human errors that should never have happened in a professional organisation with a well fleshed out and systematic processes in place . The organisation had got into a rut. If any PD has to repeat on the flight line "terminate and come back, if relight fails in the first attempt" is a guy looking for witnesses to display the fine art of a govt employee who is in the CYA mode.

A confident PD, on the flight line, would have wished the pilot: "Good luck, have a great flight" and left it at that. The rest had already been said during the briefing.

I have repeatedly said that the report is a political one and anyone can guess why.

Survival is, after all, the most basic of human instincts. Sometimes it extends to organisations too.

Be that as it may, we seem to be drawing different conclusions from the same report.

Almost all aircraft in the world have something known as the POH: Pilots Operating Handbook.

This is a mandatory cockpit reference book, sometimes spiral bound, that gives the precise procedures to follow in case of routine flight operations, start up, shut down sequence both on ground and in flight, clearcut procedures to handle in flight emergencies yada yada.

This is the SOP. The crew cannot and will not go by memory alone on how to handle emergencies or other procedures.

Too bad that the POH was never mentioned for the saras. Prototype, though it may be.

for large aircraft like the boeings/airbus, the POH is a thick book that has to be mandatorily used by the crew using a system of call and check to make doubly sure that the correct actions have been carried out and also verified to be correct.

my last on this.

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Re: Civil Aviation Development & Discussion

Postby Indranil » 08 Jan 2018 21:41

Almost all accidents are avoidable. I used to watch two series on Discovery "Moments from Disaster" and "Aircraft Accident Investigations". I don't remember of a single episode (and I have watched them all) wherein it was not a case of all holes in the cheese lining up.

NASA has undertaken flights with known but limited risks and ended up with dead astronauts. Boeing sold aircrafts with known rudder hardcover defects for close to a decade. They even tried to colour the last one of those accidents as pilot suicide and paid the family members of the deseased an undisclosed amount of money to settle out of court. Even now, they don’t know how to stop battery overheating and fires on their 787s. They have just put it in box which can contain the fire. But the alternative is that we stop flying. Nearer home, we operate Mi-17 to paradrop supplies that carry the small but still tangible risk of the parachute wrapping around the tail rotor.

PDs are always risk averse. Asking pilots to come back at the first sign of trouble is a prudent decision. An Indian PD being extra cautious in the first aircraft of its type to be developed in India is even more understandable. When Capt Bhargava expressed his reservations about the Egyptian aircraft that Messerschmitt was designing and wanted him to test fly, the latter asked him to undertake the flight and return at the first signs of trouble. It turned out that Messerschmitt (actually his engineers) were wrong. There are similar stories between the legendary Dr. Ghatge and Suranjan Das Sir. Munshi sir had flew the HT-2 and said that he had completed spin and recover in its first flight. Das sir was pushed to take up the flight because of this assertion. He said he would fly and bail out if the plane did not recover in two rotations. Das sir had to bail out! There are similar stories of the test pilots and Dr. Tank for the HF-24. He and his design team felt that using the 4 guns of the HF-24 was safe and forced the test pilot (I forget his name) to try it out. Result: a crash and severely injured pilot. How can a PD be 100% sure before a test. You can only be precautious.

And Saras also had a POH with relight instructions. It did not say feather the propeller because nobody other than the propeller maker knew. Not even P&W who gave the wrong assurance. Since then P&W have changed their manuals the world over with a footnote which says something like “Relight should occur within 30 seconds”, or something like that.

My last on this as well.

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Re: Civil Aviation Development & Discussion

Postby Suraj » 09 Jan 2018 04:11

CIDCO, GVK sign agreement: Navi Mumbai airport to be operational in 2021
As per the agreement, the commercial date of operations of the first phase of the Rs 160 billion airport has been fixed at 1,245 days from the financial closure date. The financial closure will be done six months from now which means that that the target date for launch is 2021-end. The commercial date of operations is subject to the timely completion of pre-development activities such as land fill and reclamation.

The airport will have annual capacity of ten million passengers in its first phase and is being jointly developed by GVK group-run Mumbai International Airport Limited (MIAL) and Cidco. While MIAL owns 74 per Cidco holds 26 per cent in the company developing the project. The initial concession period is 30 years which extendable for further ten years.

The airport development company will pay 12.6 per cent of its gross revenue and a concession fee ranging Rs 50 million to Rs 12.50 billion over period of sixty years to Cidco.

“Our plan is to complete the first runway by December 2019 and second runway by mid-2020. Operationalising an airport takes time and there are several clearances required including from International Civil Aviation Organisation. The three year time frame for launch is the upper limit,” Cidco vice chairman Bhushan Gagrani said.

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Re: Civil Aviation Development & Discussion

Postby Vips » 09 Jan 2018 04:46

Land Fill (flattening of hillock) is scheduled to be completed only at year end. So we have 6 months of delay right here and the new date for airport getting ready as of now (on paper) is June 2022.

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Re: Civil Aviation Development & Discussion

Postby Suraj » 09 Jan 2018 05:04

Vips wrote:Land Fill (flattening of hillock) is scheduled to be completed only at year end. So we have 6 months of delay right here and the new date for airport getting ready as of now (on paper) is June 2022.

Do you have a source for this ? The previous article report header is Jan 9. This is essentially news reported today. What is the source of your material ?

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Re: Civil Aviation Development & Discussion

Postby deejay » 09 Jan 2018 09:18

Suraj wrote:
Vips wrote:Land Fill (flattening of hillock) is scheduled to be completed only at year end. So we have 6 months of delay right here and the new date for airport getting ready as of now (on paper) is June 2022.

Do you have a source for this ? The previous article report header is Jan 9. This is essentially news reported today. What is the source of your material ?


Suraj, I have no official source but I can confirm that even the date Vips is saying will be an aggressive target to meet.

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Re: Civil Aviation Development & Discussion

Postby shiv » 09 Jan 2018 09:30

chetak wrote:have we moved away from aerodynamics and into the realm of sociology??


No offence meant but appears that the answer is yes. :D

chetak wrote:Survival is, after all, the most basic of human instincts. Sometimes it extends to organisations too.


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