Time for some Root Cause Analysis (RCA). We wont get there as we don't have access but hopefully by showing a structured approach we can steer the thought process.What happened
: About September 2, 2017 one M777 gun barrel burst/damaged during trials at PokhranWhy:
155mm shell made by OFB exploded.How do we know?
IA statement as reported by Press says Ammunition exited in several pieces. Euphemism for shell blew-up in the barrel.Evidence for above statements is shown below:
4:31 PM - 12 Sep 2017 BREAKING: M777 howitzer barrel bursts during firing tests at Pokhran. Incident took place 10 days ago. No injuries, says Army.
4:32 PM - 12 Sep 2017 M777 in Pokhran to generate Army's firing tables. In this incident, Indian ammunition exited barrel in multiple pieces causing barrel burst.
4:33 PM - 12 Sep 2017 Army: 'The barrel of the M777 has been damaged, extent of which is being assessed by jt investigation team at site.'
5 Whys?Why did the barrel burst? The shell exploded in the barrel.
Why did the shell burst? We don't know and that is the objective of the investigation.
5 Whys gives you a surface level RCA while the root cause occurs in a tree. Remember root is buried underground!
Also any RCA that blames human factors is not worth the paper its written on.
There are numerous factors, processes, procedures, design issues, schedule of events all that contribute to the accident. its like a Swiss cheese slices model. The accident is caused by the line of sight that goes through all the holes and penetrates all the barriers. Hence it is so rare.
A preliminary Fault tree for the investigation would have the following branches. If c some one can draw it up and post would be nice.Top level block M777 Gun Barrel BurstNext level 5 blocks
: Gun Shell Fuze Procedures Environment
Some times the branches will cross over as there is a combination factors but that means we don't have enough data.Branches
The branch for the Gun block will have following causes vertically down : Gun barrel material out of specifications, incorrect heat treatment of barrel, excess wear in the barrel, propelling charge ignited prematurely due to inadequate bore evacuation
Branch for the Shell will have following causes vertically down : Shell dimensional parameters out of control, Shell age out of specification, Shell corrosion at driving band, Shell storage, Shell detonated due to excess shock forces
Branch for Fuze will have Type of Fuze M572 Mechanical or Electronic Fuze : Depending on this it will have different branches. But common blocks will be Safety and Arming Device Actuated prematurely in the barrel, Firing mechanism triggered in the barrel
Branch for Procedures will have the following blocks: Inadequate procedures, Procedures not followed,
Branch for Environment will have: Temperature and air density at that time of day, Sand on the shell prevented proper seating in the chamber, Firing tempo that day (were a number of rounds fired in a short time that created schedule pressure on the crew), training of the crew
Some of the blocks are self explanatory but I think a few need some more verbiage.
The main reason the shell can burst is due to wobbling/balloting/side slap, fuze functioned before its time due to Safety & Arming being defeated and fire signal sent, and incorrect shell registering in the barrel due to procedures or debris like sand which makes the shell fall in the chamber.Some data needed:
Type of Shell :M107 or BB or EER. Each has its own factors.
What was its age and condition before firing? Any corrosion at the driving band.
What is the shell pedigree? Are there other shells from same lot?
If so can they verify any dimensions and mass properties for say ten shells to confirm they are within the parameters.
Type of Fuze :M572 mechanical or the ECIL Proximity Fuze?
What was its age and pedigree?
Charge and barrel angle:
What was the charge bag number when the accident happened? Was it minimum or maximum?
Was the barrel at low or high angle?
High angle could be a contributor if the shell did not seat properly and could fall back into the chamber. Then when the gun is fired the shell still exits the chamber and could explode in barrel or right upon muzzle exit.
Temperature and time of day. This is rare but when guns are fired cold some times the shell and fuze separate. Was seen during many night time early morning barrages.
Also did this accident happen right in the beginning or after a series of rounds were fired? Later could be due to charge debris preventing the round from seating in the barrel.
Gun: What was its condition? How many rounds were already fired? Each round erodes the barrel bore and increases the diameter so that shell side slap can occur. What is the heat treatment regimen? Repeated firings cause micro cracks in the barrel that could cause it to burst. So metallographic examination of barrel is a must. DMRL Hyderabad has awesome lab for this.
Once all this data is available , they should call in ARDE to do an analysis using their computer software for internal ballistics of the gun with actual shell parameters. Or get BAE to bring the analysis. But involve ARDE.