Investigators are recommending mandating modification of British Aerospace 146s to prevent accidental spoiler retraction, after a CityJet aircraft overran while landing at London City Airport.

Unbeknown to the crew, the spoilers did not deploy on landing despite being activated. This reduced the effectiveness of the brakes, and the crew misinterpreted the situation as a brake failure, says the UK Air Accidents Investigation Branch.

Emergency braking was applied and the aircraft's main wheels locked up over the final 473m (1,550ft) of the landing run, bursting all four main-gear tyres. The jet, which was landing on runway 10, came to a halt 50m beyond the available landing distance, and 160m from the eastern edge of the dock.

CityJet 146 skid LCY
 © Air Accidents Investigation Branch

Pilots on the 146 activate the tail-mounted airbrake and the wings' spoilers using a single lever, situated to the left of the engine thrust controls. The lever is pulled rearwards to deploy the airbrake, and then has to be pulled further back to deploy the spoilers.

But while investigators found that 14lb (62N) of force was required to pull the spoiler lever from its 'full airbrake' position on approach to the 'lift spoiler' position on landing, the reverse force needed was "close to zero".

As a result of this lack of friction, the inquiry determined that the lever could easily be nudged or vibrated out of position, stowing the spoilers. The CityJet 146's spoilers had not deployed at all, indicating that the lever moved out of position even before the activation logic conditions had been met.

While a modification has been available since 1988 to increase the lever's reverse force to 12lb (54N), this had not been incorporated on the 146 involved in the 20 February 2007 incident. The AAIB is recommending that this modification be made mandatory.

Investigators also found that the CityJet incident was exacerbated by a relatively high landing speed of 119kt, following erroneous calculations during the approach.

CityJet 146 tyre burst
 © Air Accidents Investigation Branch

Source: Air Transport Intelligence news