The airspeed of a Thomsonfly Boeing 737-300 on approach to Bournemouth airport, UK, dropped to 82kt (151km/h), the aircraft stalled, and the maximum pitch-up during the crew's go-around manoeuvre was 44°, according to an Air Accidents Investigation Branch report. The crew recovered control of the aircraft successfully and landed safely from a second approach.
No crew or passengers were hurt in the 23 September 2007 incident. The AAIB says the main cause was that the crew allowed the airspeed to decay to 20kt below the approach reference speed of 135kt because they did not notice the autothrottle had disconnected for an unknown reason after it had reduced the engine power to idle thrust for the early descent.
The captain eventually noticed the low speed and took control, announcing a go-around just before the stall warning stick-shaker operated. The lowest altitude reached during the recovery manoeuvre was just above 1,500ft (460m).
The result of applying maximum power was that the engines exceeded their full power setting, causing a nose-up pitch moment that exceeded the elevator authority, although the captain had applied full nose-down pitch on the control column. The low approach speed had caused the autopilot to motor the horizontal stabiliser to a high nose-up trim setting, and the AAIB notes that aircraft's quick reference handbook does not alert crews to the fact that trim may need to be applied to aid recovery from the stall or extreme attitudes.
One of the AAIB's recommendations is that crew should be made aware of this need.
A contributory cause of the incident, according to the AAIB, is that the autothrottle disconnect light, which is not associated with an audible alert on 737 classic models such as this one, failed to attract the crew's attention, and the agency recommends that Boeing, the US Federal Aviation Administration and the European Aviation Safety Agency should study whether the alert is sufficiently effective.
Source: Air Transport Intelligence news
