Accident Boeing 707-330B Z-WKU,
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Date:Monday 10 March 1997
Type:Silhouette image of generic B703 model; specific model in this crash may look slightly different    
Boeing 707-330B
Owner/operator:Air Zimbabwe
Registration: Z-WKU
MSN: 18930/464
Year of manufacture:1966
Total airframe hrs:85631 hours
Cycles:26912 flights
Engine model:Pratt & Whitney JT3D-7
Fatalities:Fatalities: 0 / Occupants: 53
Aircraft damage: Substantial, repaired
Location:Shannon Airport (SNN) -   Ireland
Phase: Initial climb
Departure airport:Shannon Airport (SNN/EINN)
Destination airport:Harare Airport (HRE/FVHA)
Investigating agency: AAIU
Confidence Rating: Accident investigation report completed and information captured
The aircraft was engaged on a tour of European States carrying the President of Zimbabwe and his staff. It had departed Zimbabwe on 2 March 1997 and arrived in
Dublin, Ireland on 7 March 1997. It departed from Dublin at 21.15 hrs on 10 March 1997 and arrived at Shannon to refuel, prior to departure direct to Harare, Zimbabwe.
The aircraft took off from runway 24 at Shannon Airport at 22:48 hrs. Because of the high weight the captain used maximum Engine Pressure Ratio (EPR) settings for this takeoff. Immediately after takeoff, at approximately 500 ft, the captain was alerted to a fire in the No. 3 engine by audio and visual alarms. He continued to 1,000 ft, in order to gain safe altitude, whereupon he closed down No. 3 engine and initiated fire extinguishing drill. He discharged one fire-extinguishing bottle into the engine, waited 30 seconds and then discharged the second bottle. He was informed by personnel in the cabin that flames had been seen under No. 3 engine, but that they had then disappeared. The fire warning light remained illuminated, but the captain was aware that fire damage to the detection harness could cause the warning light to remain on. He then commenced a circuit and proceeded to dump fuel as the aircraft had taken off at almost maximum gross weight and full fuel. While there were no visual indicators of continued fire in No. 3 engine, the fire warning light was still on, and he decided to dump fuel only from the opposite, left, side of the aircraft. He lowered the left fuel dump chute and proceeded to dump fuel. During this time the captain assessed his landing options.
The weather at Shannon Airport was deteriorating and there was a strong possibility that the airport would close shortly. Because of this, he did not have the option of loitering in the Shannon area to burn off fuel. Furthermore, because the B707 has only tank-to-engine cross-transfer, it was not possible to dump right wing fuel from the left wing dump chute. The captain was concerned that if he dumped 30 tons of fuel from the left dump chute to bring the aircraft weight below the maximum landing weight, the aircraft would then be suffering a lateral imbalance of nearly 30 tons, with the added complication that only one engine was operative on the heavy (right) side. The captain therefore decided to terminate the dumping after disposing of 10 tons of fuel and to land immediately thereafter at Shannon Airport.
As he lined up for landing, at about 2,700 ft, he attempted to raise the left dump chute, which failed to retract. The captain desired to raise the dump chute because deployment of the dump chute in the extended position would interfere with the selection of full flap. As the aircraft was still 30 tonnes above maximum landing weight of 112 tonnes, the captain considered that he required full landing flap for landing in this condition. Because selection of full flap would result in damage to the extended dump chute, he elected to perform an overshoot in order to sort out the dump chute problem. After the over-shoot, a further attempt was made to retract the dump chute, and this was successful. During this phase of the flight, a fault also developed in the aircraft's Instrument Landing System (ILS) display.
The captain then commenced a second approach. When he selected undercarriage down, the green lights that indicate that the main wheels were lowered and locked down illuminated, but the green indicator for the nose wheel did not illuminate. He again elected to overshoot. Minimum altitude on this approach was 1,700 ft. He selected undercarriage up. The main undercarriage retracted but the nose did not.
Noise under the cockpit indicated that the nose undercarriage doors were still open. The captain then received ATC clearance to a holding area West of Shannon to consider the situation. He considered diverting to Gatwick, where Air Zimbabwe has a maintenance base, but Gatwick was subject to deteriorating weather and other airports such as Heathrow, Dublin and Cork were already closed due to poor visibility.
Furthermore, there was continued concern regarding a possible deterioration of the weather at Shannon. When the aircraft was in the holding area, the undercarriage selection lever was moved, as normal, to the OFF position, having been previously on the UP position when the overshoot was initiated. The co-pilot then noticed that the nose green light had illuminated, indication that the nose wheel was now in the DOWN position. The flight engineer performed a visual inspection and confirmed that the nose undercarriage was down but not locked. When the undercarriage DOWN was then selected, the main wheel green lights also illuminated, and a visual inspection by the flight engineer confirmed that the nose undercarriage was now down and locked.
The captain then decided to return to Shannon. He set up a long 25-mile approach, and touched down smoothly, without any further problem. The captain turned off the runway, and stopped while the attendant crash rescue service inspected the No. 3 engine for fire. Upon receiving a "no fire" report from the on-scene crash crews, the captain decided against emergency evacuation of the aircraft. The aircraft then taxied to the terminal and the passengers disembarked normally.

1. The cause of the fire was a poorly executed welding repair of the diffuser casing in the area of the supports to the P&D Valve mounting-boss, which caused the distorting of
the boss.
2 This distortion of the boss led to an air/fuel leak, which over a long period of time caused the erosion and failure of the bolt. Then when the escaping air/fuel mixture vapour reached a critical fuel/air ratio with the vented air-flow around the diffuser casing, the mixture ignited and caused the fire.
3 The inspection of the engine, following the previous events in relation to this engine, failed to detect the true nature of the fault in the engine.

Accident investigation:
Investigating agency: AAIU
Report number: AAIU Report No. 2004-023
Status: Investigation completed
Duration: 8 years and 3 months
Download report: Final report


Revision history:


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