Investigation Summary
The investigation centered on the Hawker Siddeley HS.748's gust lock system, a mechanical arrangement designed to protect control surfaces from wind damage while parked. A critical safety feature of this system was a mechanical interlock intended to prevent the throttles from being advanced to takeoff power if the gust locks were engaged. However, investigators discovered that the gust lock lever could become partially re-engaged due to aerodynamic forces and mechanical wear. On the accident flight, non-standard repairs to the gust lock lever gate plate and gate-stop strip had created a condition where the lever could slip out of the 'unlocked' detent. During the takeoff roll, the vibration and aerodynamic loads on the elevators likely caused the gust lock to snap back into a locked position. Because the throttles were already advanced past the interlock point, the safety mechanism could not prevent the takeoff. The crew did not realize the elevators were immovable until they reached rotation speed, at which point there was insufficient runway remaining to stop the aircraft.
Final Conclusions
The Air Accidents Investigation Branch (AAIB) concluded the primary cause was the locked condition of the elevators, which prevented rotation. This was attributed to the gust lock lever re-engaging during the takeoff run, a failure made possible by non-standard maintenance and the poor condition of the gate plate and gate-stop strip. The investigation also highlighted the difficulty of offshore rescue in adverse weather and the inadequacy of lifejacket accessibility on the HS.748.
Photographic Evidence (1)
Video Analysis
Locked Into Disaster (Dan Air Flight 0034) - DISASTER BREAKDOWN — A detailed look at the maintenance errors and mechanical design flaws that led to the crash of Dan-Air Flight 0034 at Sumburgh Airport.
If playback is blocked, the owner has disabled embedding — use the link above.
Airframe & Maintenance
Crew Experience
Captain
Chris Watson, aged 37.
First Officer
Aged 51.
Systems & Failure Modes
Gust Lock System
A mechanical system of rods and cams that locks control surfaces (ailerons, elevators, rudder) to prevent wind damage while parked.
Throttle-Gust Lock Interlock
A safety mechanism designed to prevent the throttles from moving to the takeoff position if the gust lock lever is engaged.
Gate Plate and Gate-Stop Strip
Mechanical components of the gust lock lever assembly that secure the lever in the 'locked' or 'unlocked' detents.
Interesting Facts
- 01The aircraft had accumulated 29,007 flying hours at the time of the accident.
- 02The gust lock lever gate plate had undergone non-standard repairs that allowed the lever to bypass safety stops.
- 03Flight attendant Elizabeth Cowe was awarded the MBE for her bravery in rescuing 26 passengers from the sinking wreckage.
- 04The aircraft was one of seven HS.748s acquired by Dan-Air from the Argentine state oil company YPF in 1977.
- 05The passenger address (PA) system was malfunctioning and 'screeching' before departure, forcing the stewardess to use a megaphone for the safety briefing.
Safety Actions & Advisories
Gust Lock Redesign
The AAIB recommended the gust lock system be redesigned to ensure positive operation and prevent misleading indications of the lock status.
CVR Mandate
A recommendation was made to require cockpit voice recorders on all public transport aircraft over 11,400kg.
Lifejacket Accessibility
Investigators called for the repositioning of lifejacket stowage on the HS.748 to improve access during emergencies.