[Ref Flight International Magazine 12 – 18 May 2020]
Boeing is amending 747-400 flight manuals to clarify unreliable airspeed procedures after a British Airways crew erroneously believed a stall warning was genuine and repeatedly attempted a stall recovery manoeuvre.
On 9 June 2019, a BA 747-400 aircraft (G-BNLN) had reached top-of-climb at 33,000ft, during a transatlantic service to Phoenix from London Heathrow , when the crew received airspeed and altitude disagree alerts and an overspeed warning.
Three pilots, among them a training captain, were in the cockpit. While the first officer carried out the unreliable airspeed recall drill, the other two pilots checked the quick-reference handbook (QRH) to determine pitch and thrust requirements. But the aircraft’s stick-shaker subsequently activated.
The first officer reduced the pitch attitude to nose-down, and the stick-shaker ceased, but when he tried to achieve the handbook’s pitch and power settings the warning recurred. He repeated this cycle several times, and the aircraft lost about 2,800ft during the manoeuvring before the settings were reached and the stick-shaker stopped.
Although the handbook noting that erroneous alerts could occur – did not specifically mention the stick-shaker.
“This highlights the importance of clear, unambiguous information being readily available to crews at times of high workload when dealing with potentially critical incidents,” says the inquiry.