KUALA LUMPUR: COULD the extreme weather currently blanketing a large portion of the region have played a part in the disappearance of Indonesia AirAsia Flight QZ8501?
Experts, including several airline pilots, said the adverse weather formations lashing the region may have been a key factor in the aircraft’s disappearance.
The roiling clouds have been responsible for record levels of precipitation in the area and the massive deluge in the east coast states and other parts of the country.
Atlanta-based Cable News Network said some of the storm cells in the region at the time of Flight QZ8501’s disappearance reached up to an altitude of 40,000 feet, while weather monitoring network Weather Bug said lightning strikes were detected near the aircraft’s flight path between 6am and 6.20am Surabaya Local Time.
Experts, however, said modern commercial airliners are “hardened” to lighting and could withstand multiple strikes without affecting structural integrity.
It was reported that the pilot of Flight QZ8501 had requested a change in its original flight path from Indonesian Air Traffic Control because of bad weather.
“In a typical scenario, the aircraft’s cruising speed would be around Mach 0.78 or 0.79. On encountering a storm cell, the pilot would disengage the auto-throttle and throttle back to about Mach 0.76.
“This is to reduce turbulence and ensure that passenger comfort is not affected too much,” said a pilot with more than 12,000 hours of flight time on the A320 and A330.
Most of the time, pilots would weave in and around cloud formations.
In extreme cases, they would request a change in flight level to clear bad weather.
The captain said that performing a climb to get out of a storm would require a delicate balance and the almost-perfect juggling of airspeed, engine thrust and angle of attack (AoA).
AoA, or “alpha”, is the angle between the line of the chord of a wing and the relative airflow.
If a pilot exceeds the aircraft’s AoA limits, the wings would no longer generate lift and the aircraft would enter a stall.
“He’d have to work the throttles manually to find the most optimum airspeed in relation to the angle of attack.
“ It would be a matter of getting out of the storm without sacrificing passenger comfort.”
A highly placed source in the Department of Civil Aviation told the New Straits Times that an A320’s stall characteristics were relatively benign.
“Once the wings no longer generate lift, there would be a wingdrop and the nose would pitch down. Assuming the engines are not affected, it would be a simple matter of building up forward speed in a shallow dive, pull back on the sidestick controller, level off and recover.”
The A320’s engines are quite resistant to disturbed airflow and are equipped with a system called Full-Authority Digital Engine Control, which gives pilots “carefree” handling.
The DCA official also said that recovering from a stall at that altitude would have been relatively drama-free.
“They would have had enough altitude to recover from a stall. Passenger jets are not as nimble or as responsive as modern jet fighters. They’re a bit sluggish when compared with fighters in terms of response time and handling, but at that altitude, recovering from a stall would not have been a problem.
“But getting into trouble in a modern jetliner, like the A320, is very difficult, because of the safety protocols in place,” he said.
The A320 was the first commercial airliner to use Fly-By-Wire technology.
Instead of using mechanical linkages to effect changes in the flight control surfaces, the A320 uses a triplex digital flight control system that senses the pilots’ input in the sidestick controller and transmits the commands electronically to the control surfaces.
Built into the system are “inhibitors” that prevent the pilot from exceeding the aircraft’s limits.
One way for an aircraft, such as the A320, to enter a stall without warning would be if the pitot probe, or air data sensor, was blocked by ice.
The pitot probe is heated to
de-ice the system. If the probe is blocked, the airspeed reading would not be accurate.
“When this happens, you’re in a critical situation already,” said the pilot.
“It’s an emergency and you need to immediately follow the checklist. Regardless of the situation, the pilots would still have had a few seconds to issue a Mayday.”
The DCA official said this was what had happened to Air France Flight 447, without drawing parallels to Flight QZ8501.
In the 2009 incident, an Airbus A330’s pitot probe was obstructed by ice, causing the autopilot to disconnect, after which the crew reacted incorrectly. As a result, the aircraft entered an aerodynamic stall from which it did not recover. All 228 passengers died in the tragedy.