Add Category
Updated
While the Australian Transport Safety Bureau (ATSB) investigates what caused an incident on a Qantas flight that left 15 people injured, you may be wondering exactly what happened.
Aviation specialist Peter Marosszeky answered the key questions.
What is a 'stick shaker' incident?
Basically, this is a mechanism designed to warn the pilot to take control if the plane moves into a dangerous position while on auto-pilot.
If the angle of the plane changes so that the nose is too high up, it means there is not enough air flowing over the wings to create the amount of lift needed to hold the aircraft up.
"In other words [if the nose is too high up], the pilot is warned he is just about to lose control of the aeroplane."
What does it look like?
Kind of like this:
Is this an indication of auto-pilot failure?
Not necessarily. The plane could also be forced into this kind of position if there was severe turbulence, which Qantas has said was the case in this instance.
"If it was in turbulence, the aircraft could be thrown into a condition where the aircraft goes severely nose-up and the warning would be activated."
Is it serious and how often does it happen?
"Fortunately, very rarely. It is not a common thing but it is a very serious thing when it happens."
Aircraft manufacturers go to great lengths to ensure their systems work correctly and to prevent the aircraft stalling. This explains why the incident is being taken so seriously by the ATSB and the airline.
"It can happen. It has happened before.
"The stall warning is there to stop you from getting into a condition where you can't control the aeroplane.
"As to why it went to that extent, that will be a question the investigators will have to look at."
What would this have been like for the passengers and crew?
"It would be pretty eerie."
But the shaking the passengers and crew felt would have been more to do with the initial turbulence than the stick shaker warning, Mr Marosszeky says.
"The shaking … I don't think there is an issue of shaking of the aeroplane, that would be a turbulence-related thing.
"To be thrown around like that and have the aeroplane shake, that suggests that it is a weather condition that caused that."
Was the plane in a particularly bad spot for turbulence?
While there have been numerous cases of severe turbulence around Hong Kong, Mr Marosszeky says that has more to do with pilot error.
"In a lot of the cases, there has been an issue with pilot error. There have been issues with the aircraft's mechanical condition or electronic conditions.
"But in this particular case, I would say with the Qantas aeroplanes, you would have to consider weather conditions first as being the major causal factor.
"There could be other things in the system that caused the problem but pilots would normally have to disengage the auto-pilot and recover manually."
Does the aircraft have a good safety record?
The plane in question was a Boeing 747. This is how Mr Marosszeky described it:
"Excellent. One of the best in the world. It is a remarkable piece of machinery."
So that's a yes. Mr Marosszeky says even given the plane's age — about 17 years old — the onboard technology would still have been world-class.
"The auto-pilot systems don't change in principle very much. The technology that goes into producing them changes.
"The reliability is still as good as the new stuff that is coming out.
"There is really no issue of reliability or system failure, premature failure. It is an infrequent issue when it comes to the big aeroplanes."
Will investigators focus on the use of auto-pilot?
Actually, Mr Marosszeky says using auto-pilot is the most common way to land the plane. So this is not likely to be the main focus of the investigation.
"There is another way experts could look at this — the aircraft is very large. For it to be thrown around so severely [that] it gives you a stall warning, that is unusual."
He also says the turbulence occurring at the time will be a major factor.
"There is turbulence involved so that is a link they would have to be seriously considering. This will come to the fore when they do the investigation and go through the black box."
Will we find out what the ATSB investigation concludes?
"Yes, the ATSB will get to the bottom of it. Reviewing the digital flight data recorder will give up a lot of the stories that really need to be addressed."
That report is expected to be released in August.
Topics: air-transport, air-and-space, accidents, disasters-and-accidents, air-transport, safety, occupational-health-and-safety, hong-kong, melbourne-3000, melbourne-airport-3045
First posted