Additional Thoughts on AirAsia 8501
Additional Thoughts on AirAsia 8501
https://www.rayjayperreault.com/wp-admin/post.php?post=418&action=edit
This link points to one of my previous posts where I presented a possible scenario for the tragic loss of AirAsia 8501. Unfortunately, my comments may turn accurate.
To summarize, ice can cover part of the Pitot/Static system and cause it to malfunction. I won’t go through the math again (see the link), but the first item to ice over is usually the static port, which is a small hole on the side of the fuselage. If this freezes over the airspeed in the cockpit will increase. If it freezes quickly, the indicated airspeed can increase dramatically.
First off, normal procedures call for the Pitot/Static anti-icing system to be on in icing conditions. It is electrically heated and it can fail or not get turned on. In severe icing conditions, it can accumulate ice regardless of the heating. I’m not sure about the airline procedures in this case. Some have the anti-ice on at all times in flight, and some are automatic when the plane encounters icing conditions.
Regardless of the status of the system if a pilot sees a dramatic increase in airspeed he might assume a descent and if he doesn’t check the other gauges he might pull the nose up to slow down. If the airspeed continues to increase he might pull the nose up further and the G forces can feel the same as if he were pulling out of a dive.
If the nose continues going up and the ice continues to accumulate, it might reach a stall angle of attack and because of the ice it may stall asymmetrically and fall off to one side. Most airliners will stall with the wings level and the nose dropping, but because of the ice, one wing might drop. If the wing continues to drop, the nose will drop also. In a short time, the airplane can be pointing straight down and soon it will exceed its design limits and it would be almost impossible to regain level flight once the nose is pointed down.
A rapid descent through a thunderstorm would be very disorientating and difficult for recovery. Depending on the amount of ice, its location and other factors structural damage may occur which makes the recovery even harder. The plane could get into a spiral where it doesn’t come apart, but it is unable to recover aerodynamically. If that happens it would hit the ocean at a very high descent rate.
Pilot’s are trained to look at all of the gauges and make sure they understand any unusual indications. Anytime something doesn’t look right, the pilot can verify it with the other indications. In this scenario, the pilot would look at his artificial horizon to verify that the plane is level. Then he would look at the engine indications to make sure the engines were performing. In icing conditions, he should verify that the appropriate anti-icing and de-icing systems are working. In addition, the pilot should look at an instrument called a VVI, which indicates if the plane is climbing or descending. If all of them indicate level flight then Pitot/Static icing is the problem and they have to get out of the icing conditions immediately.
This type problem is one of the more subtle emergencies that can sneak up on a pilot. There are some, where you’re all ‘arms and elbows’ and there are some, where you take your time and figure it out. In another one of my posts, I say the first thing a pilot should do in an emergency is ‘wind the clock.’ Take the time to make sure they understand the problem.
Terrible accident.
Ray Jay Perrault
