PIA F27 at Multan on Jul 10th 2006, engine failure and stall on departure

Last Update: May 25, 2012 / 20:41:38 GMT/Zulu time

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Incident Facts

Date of incident
Jul 10, 2006

Cause
Engine failure

Airline
PIA Pakistan International Airlines

Flight number
PK-688

Departure
Multan, Pakistan

Destination
Lahore, Pakistan

Aircraft Registration
AP-BAL

Aircraft Type
Fokker F-27 Friendship

ICAO Type Designator
F27

A PIA Pakistan International Airlines Fokker F-27-250 Friendship, registration AP-BAL performing flight PK-688 from Multan to Lahore (Pakistan) with 41 passengers and 4 crew, had just departed Multan's runway 36, when tower and other ground observers saw the aircraft at very low altitude in a right turn. Tower attempted to contact the aircraft but did not receive a reply. A phone call from a local resident about 2 minutes later confirmed the aircraft had crashed about 2km northeast of the runway. The aircraft was consumed by a ground fire, all occupants of the aircraft perished in the crash.

Pakistan's Civil Aviation Authority released their final report concluding the probable cause of the accident was:

Accidents and losses are part of aviation business, but avoidable accidents hurt us the most. PIA or any other company can ill afford such losses. In this accident, while the aircraft had developed a problem in its right engine turbine, resulting in the engine failure, yet a professional handling by the aircrew could have saved 45 precious lives and a valuable aircraft.

It is also felt that this accident may not be viewed as an isolated case of a pilotÂ’s failure to handle the emergency. The problems were observed to be complex and deep routed and reflect towards the organization and her culture. The occurrence (right engine failure) took place due to improper assembly during over haul. Quality Control system of PIA Engineering appears to be in affective in detecting the weaknesses. The accident took place due to improper handling of the emergency by the air crew which reflected towards inadequacies of PIA Training/Assessment and Scheduling System. The CAA Airworthiness, too, can not be absolved of their responsibilities of regulating and monitoring the quality control system at PIAC Engineering.

The investigation commission reported that the investigation was unable to ascertain the takeoff weight of the aircraft. While the relevant documentation does not suggest takeoff occurred above maximum takeoff weight the possibility of such a takeoff above maximum takeoff weight could not be ruled out.

The weather was good and did not contribute to the accident.

The aircraft began to accelerate on runway 36. About 5-6 seconds prior to reaching V1, about 4000 feet down the runway at a speed of 90 KIAS (V1: 108 to 110 KIAS), the crew noticed a right hand engine's deviation from the required torque pressure, the engine began to spool down, the takeoff was continued. The aircraft veered to the right before paralleling the runway center line close to the right runway edge. At 120 knots (Vr=109 knots) the aircraft rotated, just after the begin of the rotation the right hand propeller feathered as result of the torque reducing below the limit for autofeather. The aircraft became airborne about 6800 feet down the runway, much farther into the takeoff run than normal. 11 seconds after the torque began to reduce the crew manually feathered the right hand propeller. The aircraft crossed 35 feet AGL about 45 seconds after beginning the takeoff run (normal expected time 38 seconds). The aircraft initially climbed at a higher climb rate than recommended for single engine departures and reached a maximum height of 160 feet AGL maintaining 120 KIAS, the speed subsequently reduced until the aircraft entered a stall at 85 KIAS 10 seconds later, contacted trees, impacted ground in an inverted attitude, got stuck in a mud wall and burst into flames. Emergency services reached the crash site 10 minutes later, fire fighters extinguished the fire soon after.

The investigation commission reported that following the accident a runway inspection revealed metal debris on the right side of the runway, between 4000 and 6800 feet down the runway, which was identified to originate from turbine blades of the right hand engine. The tracks on the ground suggested the aircraft veered to the right about 4000 feet down the runway and subsequently paralleled the runway center line to the right of it.

The rest of the aircraft came to rest in a confined area at the crash site. Examination of the debris revealed:

- Flaps were retracted
- nose and main landing gear struts were extended
- the oxygen and fire bottles were discharged as result of the ground fire
- no evidence of sabotage was found
- no evidence of an inflight fire was found
- no inflight structural failure or any primary or secondary surface
- the right hand engine appeared to be at low rpm at impact producing no power, the right hand propeller's two blades were in the feathered position
- the left hand engine was rotating a high speed, the propeller blades were bent
- the damage to the left hand engine and main bearing was different to what was to be expected from rotational damage at impact
- no evidence of a bird strike incapacitating the flight crew was found
- an extensive post impact ground fire was fed by the aircraft's fuel

The investigation determined that all occupants of the aircraft died instantly as result of the impact forces. The post impact fire was so intense that even if there had been survivors of the initial impact no-one on board could have survived the fire.

The investigation highlighted that although the aircraft had been certified as airworthy, the "procedure for issue of certificate of airworthiness is inadequate and weak to ensure that aircraft is maintained in accordance with Technical Literature" effectively putting into doubt that the aircraft was airworthy. The investigation added, that the last review of the aircraft for renewing certificate of airworthiness was done by an engineer with avionics background only.

The investigation commission added pressure stating: "It is the opinion of the inquiry committee that present procedure of C of A cannot ensure that aircraft is maintained in accordance with Technical Literature and there is no Service Bulletin or Mandatory Airworthiness Directive (AD) outstanding. The inspection by Airworthiness for renewal of C of A is also a weak area."

The investigation highlighted that for example the right engine's feathering motor was found in a poor condition of maintenance with wrongly fitted bearing and worn out armature, PIA's engineering did not possess diagrams of the CVR and DFDR for maintenance, the engine oil condition had not been monitored by any Spectrometric Oil Analysis Program and the oil was extremely dirty.

A tear down examination of the right hand engine revealed that the "thrust bearing of right engine was improperly assembled during last overhaul at DART Engine Shop PIAC in September 2005." The thrust bearing assembly had been turning eccentric while being assembled and thus was orbiting instead of an ideal rotation. The resulting imbalance caused reverse bending loads on the bold heads of the bearing assembly resulting in the failure of one bolt head, which created even more stresses and caused the bearing housing to open after the next 5 bolts had failed. The rotor assembly of the turbine increased its radii of orbit and caused the turbine rotor to free itsself and move forward resulting in the turbine discs and blades to experience heavy rubbing, the turbine blades failed due to resulting thermal stresses and broke away.

The investigation determined "PIAC Engineering, Quality Control, failed to detect improper assembly of thrust bearing during last overhaul."

The investigation commission stated that following the engine failure, which was first observed at about 90 KIAS, the crew made following omissions in handling the emergency contrary to standard operating procedures:

- the crew did not rejected takeoff despite clear indications of an engine anomaly below V1
- did not declare emergency (internally and externally)
- did not retract the landing gear
- started the engine feathering drill below 400 feet AGL instead of taking positive control of the aircraft
- did not maintain runway direction, the resulting turn added to the speed reduction
- "The actions of aircrew lacked professionalism, a poor display of airmanship and an extremely poor emergency handling."

The investigation released 11 safety recommendations focussing mainly on maintenance procedures, maintenance quality assurance and regulatory oversight monitoring maintenance.

As last point the investigation recommended: "Those who failed to perform during overhaul of the engine and carrying out quality inspection and issued Certificate of Airworthiness, should be proceeded against under the existing Rules."