A Lockheed L188C (Lockheed Electra) took off, shortly before from London Stansted (England) Runway 05 on this day in aviation history.
Onboard the pilots and a company engineer as well as the cargo, giving the aircraft a take-off weight of 97.388 lbs (44.174 kg).
The failed power supply circuit board in the propeller synchrophaser unit © aaib.gov.uk
After a smooth take-off run the aircraft rotated and lifted off the runway. As soon as the aircraft became airborne the crew noticed a yawing, pitching and rolling movement of the aircraft combined with a hunting and fluctuating noise from the propellers. The rpm of the engines was fluctuating ~1000 rpm as well as various other engine indications that were not indicating a stable value. Picture left; X-ray of the failed power supply depicted above. The engineer pointed out to the crew that the #2 & #4 engines were well over the take-off limit at 1080 ºC (limit 971 ºC). Power on these engines was reduced immediately, to bring the temperatures back in limits.
For all onboard the aircraft this was something they never encountered before, attempting to identify the cause of the problem. The #2 engine had to be shut down as the rpm dropped below the operating range. As the aircraft climbed through 300o feet a PAN PAN call was made to ATC, stating the situation and requesting vectors back to Stansted. Reading of the checklists was difficult because of the erratic movement around all axis of the aircraft. power lever adjustments had no effect as the engine parameters continue to fluctuate. The propellor of engine #3 was found to be "stuck" at ~14.300 rpm (~500 rpm higher than normal). The crew decide to let it run and shut the engine down on short finals. Now on the downwind leg for the return to Runway 05, the crew slowed the aircraft down to 190 kts by reducing the power on engines #1 and #4. The flaps were set to 78% and at 7 nm from the runway engine #3 started to show signs of recovery. When the aircraft slowed down to 170 knots the flaps were selected to 100% in preparation for the planned 2 engine landing at a speed of 150 knots. With the aircraft on the approach for a landing on Runway 05, at an altitude of 100o feet, the engines #1 and #3 appeared to flame out.
FDR Data from the incident flight ©aaib.gov.uk
The #4 engine was pushed to the limit while the propellor rpm was still fluctuating. With only one engine operating they slowly got below the normal approach path and crossed the threshold with the PAPI showing three red and one white with the speed decaying towards 130 knots. The aircraft touched down just short of the touchdown zone and slowed down on the runway exiting the runway via a high-speed exit. Once clear of the runway the aircraft was brought to a stop. The fire handles for engines #1 and ## were pulled as they were hot. The normal checklists were completed and the last running engine, engine #4 was shut down normally. The incident was investigated by the Air Accident Investigation Branch and they drew the following in their report (the report is available by clicking here);
The cause of the incident was a failure within the power supply circuit board in the propeller synchrophaser unit*). This caused significant power and rpm fluctuations on all four engines giving the flight crew difficulty in handling the aircraft. The No 2 engine exceeded its maximum governed speed which resulted in the fuel flow to the engine being cut back by its governor; this led the crew to believe that the engine had begun to run down and they shut that engine down. The remaining engines continued to fluctuate and, on the final approach, the No 1 and 3 engines also appeared to run down, probably due to fuel being cut back after overspeeding.
*) The synchrophaser is used to synchronise the 4 propellers, normally it is switched off for take-off and landing.
Note for those readers with an interest in Dutch aviation history, this aircraft was delivered on 25-02-1960 as PH-LLG to KLM Royal Dutch Airlines, in 1968 it flew for Dutch charter operator Martinair for 9 months. (see the picture below)
Source https://avia-dejavu.net © unknown
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