There is one scenario that pilots and passengers alike fear when it comes to flying – the aircraft stalling. What does it mean when a plane stalls and are you in any danger as a passenger? Let’s discuss this unthinkable event.
What is stalling?
We begin with a definition of what stalling is in the context of an aircraft in flight.
When a plane flies, the air around the wings is at different pressures. The air passing over the wing has a lower pressure than the air passing under the wing, generating lift and ‘pushing’ the aircraft upwards. However, when an aircraft increases its ‘angle of attack,’ known as the angle at which the wings face oncoming air, a separated flow of air is created behind the wings where the two air pressures mix. At a certain point, the separated flow reaches a critical mass that stops lift generation.
Without lift, the aircraft will start to fall no matter how powerful the engines are or how fast it flies. The point where an aircraft wing reaches stalling conditions by raising the nose of the plane is called the critical angle of attack. It is generally over 15 degrees, hence why you rarely see aircraft take off or land at a steep angle.
While every stall situation is different, the general advice for pilots to recover from a stall is to lower the nose of the aircraft (and thus decrease the angle of attack) and increase speed.
What happens when a commercial plane stalls?
There are there three main scenarios for when a commercial aircraft will encounter a stall.
- During takeoff and landings, when the plane is moving slowly and has a high angle of attack, especially when an aircraft is turning on the final approach or turning just after takeoff.
- Stalling may also occur when an aircraft has been ordered to ‘go-around‘ and abort a landing. The pilot must transition from a low airspeed to a high airspeed but also trim the angle of attack and turn the aircraft.
- When ice, dust, or other materials cover a wing, the rougher surface creates a higher angle of attack and makes the aircraft more susceptible to stalling. This is one of the reasons why de-icing an aircraft is vital in winter.
Is it dangerous for passengers when an aircraft stalls?
The biggest question for many reading this article is if there is any significant risk of aircraft today of stalling. With all the high-tech autopilots and extensive training, are you in any danger of stalling while in flight?
Unfortunately, we only need to look at Air France flight 447 in 2009 to see what happens when a commercial aircraft (Airbus A330) encounters stall conditions. The plane was en route to Paris, France from Rio De Janeiro, Brazil, when ice crystals clouded the airspeed sensors and disabled auto-pilot systems. Pilots then mistakenly increased the angle of attack of the aircraft, causing stall conditions, and plunging the plane into the ocean.
All passengers and crew on board perished instantly.
The aviation industry learned several lessons from this event:
- Warning messages failed to alert the crew or provided incorrect feedback. The angle of attack was so extreme that alarms disregarded the readings as false. When pilots lowered the nose, alarms kicked back in as the angle of attack data was now more ‘reasonable.’
- A lack of training for pilots flying at a high altitude and losing airspeed indicators
False readings told the pilots that their aircraft was moving slowly and thus in a stall. In retrospect, had the pilots not taken any action when the auto-pilot disabled, or lowered the nose back to level when stalling, the airspeed would have increased with a lower angle of attack, and the aircraft would have remained in the air.
Since the event, Airbus has told airlines to switch at least half of the sensors onboard the A330 and A340 to a different supplier to ensure they cannot be iced over.
“We issued an AIT (Accident Information Telex) a few minutes ago recommending that A330 and A340 operators fit at least two probes supplied by Goodrich,” Airbus spokesman Stefan Schaffrath said to Routers back in 2009.
The incident is now also taught to commercial pilots, so they can recognize stall conditions when flying at a high altitude.
What do you think? Let us know in the comments.
