Coltishall Incident - XM188

By C. Carver

Background technical information for non –riggers.

The Lightning hydraulic system basically consisted of 3 main systems, namely No 1 & 2 Controls and Services. Each Control system was independent of the other. The Services were supplied by pumps on both No 1 and No 2 engine and can be consider as one system.

There were no gauges in the cockpit for the Controls systems, low pressure would be brought to the pilots attention by means of red lights on the Central Warning Panel (CWP), and “attention getter” lights.

There was a gauge for the Services hydraulic system pressure. This gauge, mounted on the combing, was about 1 inch in diameter. At the 7 o’clock position was a white mark, above that at 8 o’clock was a red mark. At approx. 2 o’clock position was 3000psi mark. If the needle was on the white mark it was an indication of “no power” to the gauge. If the needle was on the red mark it indicated gauge was powered but no hydraulic pressure.

An hydraulic accumulator is a pressure storage reservoir, placed in the hydraulic system to provide a reserve of power for limited operations in the event of system failure. Pressure in an accumulator is prevented from flowing “upstream” by using a non-return valve, thereby reserving the pressure for that particular sub system in which it is installed. The Lightning Mk1A is steered on the ground by using differential braking .

Thursday 20 June 1968

The line reported to Aircraft Servicing Flight (ASF) a hydraulic leak from the vicinity of “D” door undercarriage jack. I was in the office when this call came through and said I would take on the task of rectification. The aircraft was brought into the hanger, The door jack was replaced, aircraft jacked up, leak checks and functional checks carried out and signed off as serviceable.

Friday 21 June 1968

The aircraft completed a normal sortie.

After turning off the runway, the pilot shut down No1 engine and started to taxi, using power from No2 engine. After negotiating several bends in the taxiway, the aircraft approached the hangers. Trying to slow down before the next bend, the pilot realised he had no brakes.

Looking at the Services pressure gauge he noted the position of the needle being at 8 0’clock, but mistakenly assumed he had no electrical power to the gauge, because he did not have enough RPM from the engine and the generator was “off line”. He therefore increased the power on No 2 Engine to bring the generator “online” hoping to see the gauge showing hydraulic pressure.

Realising that he could not stop the aircraft, and it was going to hit the hanger wall, self-preservation took over. He undid his straps and opened the canopy. (Canopy opening is supplied from the Services system and there was an accumulator to provide the power.)

When the aircraft struck the hanger, the pilot hit his face against the windscreen arch, causing some teeth damage. He was able to extract himself from the aircraft and get onto the hanger office roof, make his way to a ladder at the far end of the hanger and climbed to the ground.

The aircraft was now against the hanger wall at a very small acute angle, with the engine running at approx. 80% power. The ventral tank holding bolt had sheared and the tank was detached from the aircraft. The crash caused the inertia switches to operate and shut off all electrical power.

Various attempts were made to shut the engine down, by throwing switches in the cockpit, but without power this was not possible. The throttle could not be closed because the linkage had been jammed by the crash.

The engine was NOT shut down by the BAC rep or a Sergeant fireman, contrary to versions I have read.

After the engine had been running for approx. 20 mins:- Chf Tech Dave Munroe, an engine fitter, bravely went between the aircraft and the hanger wall, removed a panel just below the wing, removed a split pin, undid a nut and removed a bolt from the Low Pressure Fuel Cock final linkage to the engine and shut the engine down.

As far as I can recall for his actions that day he only received a “Well Done” certificate

A Board of Enquiry was set up.

Tuesday 25 June 1968

At about 10am that day, I was summoned to attend the Board of Enquiry.

I was a young corporal, 2 years out of Halton.

For the rest of the day, I was questioned about my knowledge of hydraulic systems, the effect of air in systems, what training I had received, how the rectification work had been carried out, how the system was bled of air, and so on and so forth. The Board made great play of the fact I could not specifically say who had authorised me to carry out the rectification work. The atmosphere was very frosty and felt like an interrogation.  I was very intimidated sitting before a Wg Cdr and two Sqdn Ldrs. At about 6pm the Board ask me to leave the room and wait outside.

After 30 minutes I was asked to return, and I was informed that the Boards initial findings on the cause of the accident where that the brakes failure was a result of the hydraulic system not being properly bled of air the day prior to the accident. As a result of this I was considered to be negligent, and my reputation was in jeopardy. I was then given a formal caution. Due to legal requirements I was informed that I now had the right to hear and see all evidence taken to date, by the Board and to ask questions of the witnesses.

I elected to have all witness statements read to me.

Wednesday 26 June 1968

08.30

The Board President again asked me if I wished to have all previous statements read to me, which I affirmed, the Board President was unhappy with this and repeated his question, to which the answer was still yes.

Most of Wednesday was taken up by hearing all previous statements.

Thursday 27 June 1968

O8.30 I sat with the Board as more statements were taken, OC Eng, Flt commander, Sqn commander, firemen, medics etc etc.

Friday 28 June 1968

08.30

More statements

10.00

I was asked to leave and return at 13.30

13.30

Upon returning  was told I was no longer required, no reasons given.

I found out sometime after, that the Board had received a report from BAC that a non-return valve on the No1 Systems pump had failed, this allowed pressure from the No2 Services systems pump to bypass straight to return, thus not pressurising the Systems hydraulic system.

As soon as the pilot cut No 1 engine, the Services system pressure would have rapidly decreased to zero. Using the reserve pressure in the brake accumulator, the pilot was able to steer around most of the taxiway until that pressure dissipated.

My thanks to Chf Tech Foster who lent me his very polished shoes on the first day I sat before the Board. Mine were black but oil and fuel stained.

All the staff in ASF who gave me support and advice.

Also, to the members of ASF who kindly washed all the Sahara red dust off my car whilst I was before the Board, and to the party in the NAAFI that night.