Investigation Summary
The investigation centered on the failure of the port flap operating rod, which was found to have succumbed to metal fatigue. This failure allowed the port flaps to retract while the aircraft was in a high-lift configuration for landing. Due to the design of the flap compensating mechanism, the retraction of the port flaps caused the starboard flaps to extend even further, creating a massive lift imbalance. The resulting roll to the left was so severe that the wing tip and landing gear struck the grass beside runway 28R. Although the crew applied power to attempt a go-around, the asymmetry was insurmountable. The aircraft collided with parked British European Airways aircraft, including G-ARPI and G-ARPT, before coming to rest upside down against the terminal. The subsequent explosion and fire destroyed the aircraft and a significant portion of the parked Trident G-ARPT.
Final Conclusions
The Department of Transport concluded that the primary cause was the fatigue failure of the port flap operating rod. The investigation noted that the design of the compensating mechanism exacerbated the roll by further extending the opposite flaps when one side failed. The report stated it was doubtful that any pilot action could have prevented the crash once the rod failed, given the 25 seconds required for flap retraction and the extreme bank angle generated by the asymmetry.
Video Analysis
BKS Transport Flight C.6845 Crash & Aftermath Footage — Historical footage and overview of the 1968 Heathrow crash involving an Airspeed Ambassador horsebox transport and parked Trident aircraft.
If playback is blocked, the owner has disabled embedding — use the link above.
Crew Experience
Captain
Captain Ernest Hand; Fatal
First Officer
Second Officer John Burchell; Fatal
Systems & Failure Modes
Flap Operating Rod
A mechanical linkage that controls the extension and retraction of the wing flaps; the port rod failed due to fatigue.
Flap Compensating Mechanism
A system designed to balance flap movement which, in this failure mode, caused the starboard flaps to extend further when the port flaps retracted, worsening the roll.
Interesting Facts
- 01All eight racehorses on board, belonging to businessman William Hill, were killed.
- 02The parked Trident G-ARPI, which lost its tail fin in this accident, was later repaired only to be destroyed in the 1972 Staines air disaster.
- 03The parked Trident G-ARPT was damaged beyond economic repair after its entire tail section was sliced off.
- 04The Vickers Viscount G-APKF received slight damage and was repaired, but was later destroyed in a fatal hull-loss accident in Cambodia in 1975 while operating as XW-TDN.
- 05Testing of other Airspeed Ambassadors following the crash revealed similar fatigue cracking in flap operating rods.
- 06The aircraft involved, G-AMAD (construction number 5211), first entered service in 1950 and was formerly named 'Sir Francis Drake' while in service with British European Airways.
Safety Actions & Advisories
Fleet Grounding and Inspection
All Airspeed Ambassadors were grounded immediately following the accident for inspections of the flap operating rods.
Flap Rod Strengthening
Flap operating rods on the remaining Ambassador fleet were fitted with steel reinforcements, increasing their certified service life to 37,000 hours.