Analysis: Experts debate loss of AirAsia Indonesia Flight 8501

Aviation disaster experts are debating several long-standing safety issues as the disappearance of AirAsia Indonesia Flight 8501 is a seen as a victim of bad weather.

Unlike the doomed Malaysia Airlines MH370 or even the shot-down MH17, where circumstances are beyond the normal, most commercial-air crashes have more mundane expanations.

These include malfunctions caused by ice and high altitudes when flying through clouds and rain.

The region is well known for severe monsoon storms at this time of the year and meteorological reports show severe weather reaching well above 40,000ft.

AirAsia chief executive Tony Fernandes has said, “The weather was not good,” adding that while flying at roughly 32,000 feet the pilots of Flight 8501 asked air-traffic controllers for permission to climb due to “storm clouds.”

At this point experts says there is a possible danger of ice accumulation. Ice particles embedded in intense, high-altitude storms have caused airspeed indicators – called pitot tubes – to malfunction and contributed to fatal jetliner crashes over the years.

The best-known example occurred on Air France Flight 447, an Airbus A330 that crashed in June 2009 en route to France from Brazil, killing all 228 people aboard.

Investigators determined that while flying through an area known for strong, high-altitude storms, the Air France pilots failed to react properly to unreliable airspeed indicators, allowed the plane to slow too much and failed to get out of a deadly stall because they kept pulling the jet’s nose up at a sharp angle.

The A330 plummeted into the Atlantic Ocean from roughly the same altitude as the last position controllers saw on their radar screens for Flight 8501, an analysis by the Wall Street Journal shows.

After Flight 447, European air-safety regulators issued safety directives mandating replacement and upgrades of pitot-tube systems on Airbus jetliners, including A320s.

In October, they issued a new mandate giving operators two years to make certain modifications, because initial replacement parts didn’t demonstrate the necessary “level of robustness to withstand high-altitude ice crystals.” It isn’t clear whether the AirAsia aircraft was covered by that mandate.

Robert Francis, former vice chairman of the US National Transportation Safety Board, says the Air France example is the likely reason at this early stage of the investigation for the apparently sudden loss of control, because modern jets are designed and maintained to withstand even severe turbulence without parts breaking or falling off.

When airspeed indicators malfunction, the autopilot typically kicks off and pilots are then forced, at least temporarily, to manually fly the plane. Prompted by Flight 447, airlines stepped up training of pilots to help them cope with such situations at high altitudes.

“Flying five miles or more above the earth also raises dangers of stalls or upsets in which engines and flight controls act differently than in normal circumstances.” the Journal says.

“In one prominent accident in 2004, a Pinnacle Airlines regional jet, flying at night without passengers, climbed dangerously high and the crew failed to fully understand the handling characteristics in the unusually thin air. Both pilots died when the engines stopped putting out thrust and couldn’t be restarted, and the plane crashed into a residential area in Missouri.

“For Airbus jets, handling issues are exacerbated because some of the computerised safety limits pilots routinely rely on suddenly can disappear if speed sensors are blocked or inoperative.”