Accidents involving aircraft cruising through tropical or sub-tropical zones – like AirAsia flight QZ8501 in December – are happening often enough now for the industry to have cause to refresh pilots on the risks. Therehave been three accidents in similar circumstances over the last 10 years.
When the Air France flight 447 accident report was published in 2012, French accident investigator BEA warned of the need to prepare pilots for high altitude aircraft handling – and comparisons with the AirAsia Airbus A320 accident in December have highlighted this apparent area of operational weakness.
But now that Indonesian accident investigators have formally stated they will not publish a preliminary factual report about flight QZ8501, it could be up to two years before operators know whether BEA's concerns are reflected in this case.
There have been three other accidents in the last 10 years that merit comparison with the flight QZ8501 incident over the Java Sea. These four accidents all took place during cruise in tropical/subtropical zones, and in all cases the crews were manoeuvring to avoid bad weather. In all four cases control was lost, and none of the crews made an emergency call.
Before the AirAsia loss in December, there was the Swiftair/Air Algerie McDonnell Douglas MD-80 loss over Mali last July, Air France Airbus A330 flight AF447 over the South Atlantic in June 2009, and West Caribbean Airways’s loss of an MD-80 series aircraft over the Caribbean Sea in August 2005.
Looking back further in the archives, jet accidents with this combination of circumstances did not happen – although flights in those days were just as likely to have to fly through the tropics as they are now. Tropical weather seems to be a “modern” accident trigger, in the same way that loss of control in flight (LOC-I) is now accepted by ICAO as the greatest aviation risk to life, when before the 1990s it was not.
There is an uncanny similarity between the onset of problems in the AirAsia and Air France cases. Both pilots suddenly selected a nose-up attitude that gave them a rapid rate of climb – estimated to be 6,000ft/min in the AirAsia case, and known to be 7,000ft/min for AF447 – at an altitude where demanding such performance from the aircraft is unrealistic. In the Air France case the aircraft was in a full stall within 46s, and the crew did not apply stall recovery procedures.
When it published pilot training recommendations in the AF447 official accident report,BEA called for a list of actions to be implemented. These including training in stall recovery at high altitudes as well as low, practicing flying in alternate and direct control law as well as normal law close to the edges of the flight envelope, carrying out flying exercises to test whether pilots understand aerodynamics in practice, as well as in theory, and introducing more surprise events into recurrent training scenarios to prepare pilots – individually and as a crew – to react calmly to the unexpected.
Pilots are instructed not to disconnect the autopilot at high altitudes for good reason: with reduced vertical separation minima applying above 29,000ft in most parts of the world now – and handling being a delicate matter at high altitude – manual flying is banned there. BEA points out, however, that if the automatics trip out – as they did in the case of AF447 – the pilots have no choice, so they should be reminded in the simulator of what handling is like up there.
Pilots talk glibly on Internet forums about “Coffin Corner” – as applied to the aircraft’s narrowing flight envelope when it approaches the high altitude edges of its performance capabilities – but according to BEA they need to be reminded of what to do if the edges are actively breached, because recovery is almost always possible if the correct procedures are applied.
Source: FlightGlobal.com
