The incident on Singpore Airlines flight 321 last week has been making the headlines for the past week, and at TravelGuys we’re not too keen on surfing on such dramatic events to gain traffic.
Not surprisingly, a number of media weren’t shy about it. But there’s a difference between the duty to inform and sensationalizing, especially by telling untruths or misrepresenting figures out of context.
It’s because we’ve heard so much from people close to us about this event, impressed and even shocked by what they’ve heard in the media, that we’ve decided to make a few things clear.
This is, of course, an article for the general public, and we don’t claim to be experts on aeronautical phenomena. If pilots or other specialists wish to contribute their own thoughts on the subject, the comments are of course open to them.
The SQ321 incident
We’re talking about flight SQ321, operating between London and Singapore on May 20. The aircraft, a Boeing 777-300ER, encountered severe turbulence over Burma, resulting in injuries to some 30 passengers and the death of another passenger, probably from a heart attack.
The aircraft was diverted to Bangkok, where the injured were treated.
A few words about turbulence
Since turbulence is such a hot topic of conversation, it’s a good idea to take a few moments to recap on the subject. For a more in-depth look at the subject, we refer you to our previous article on turbulence.
They’re also mistakenly called air pockets, but there’s no such thing as an air pocket any more than there’s a water pocket in a wave pool: they’re simply air flows pulling the plane up or down.
There are 3 main types of turbulence, and the ones we’re interested in here are clear-sky turbulence, so called because it’s undetectable, unlike weather-related turbulence, for example, which can be seen on radar. They occur when winds moving at different speeds meet and form eddies.
[Note: information is gradually becoming clearer, and it seems that the turbulence was caused by the crossing of a cumulonimbus cloud].
This is the type of turbulence encountered by flight SQ321.
Turbulence is very unpleasant for passengers, which is why pilots avoid it whenever possible. As for their dangerousness, there are two ways of looking at it.
The first, which should reassure you, is that they are not at all dangerous for the aircraft. They are designed to withstand enormous turbulence, which is why their wings are so flexible.
There has never been a plane crash due to turbulence. In fact, there are two that we explain in our article on turbulence, but they are wrongly attributed to the turbulence itself: it was piloting errors that led to the fatal outcome, not the turbulence itself.
However, while aircrafts are highly resistant to turbulence, this is not the case for their contents, i.e. the passengers. A movement of just a few centimetres upwards or downwards can throw a passenger into the air. A bit like driving over a speed bump and lifting off your seat. Well, turbulence is like speed bumps at 950km/h… a few centimetres higher for the car, but much more for the passenger.
This friendly steward explains it very well in another way in this video.
That’s why you’re always asked to keep your seatbelt fastened in flight, even in the absence of turbulence, because when turbulence does occur you’re unlikely to have time to buckle up, and that’s certainly what happened to those injured on the SQ321. And that’s certainly the most important lesson to be learned from this incident: never, ever unbuckle your seatbelt.
And if you were impressed by the damage to the aircraft’s cabin, particularly to the baggage compartments, you should know that it was caused not by turbulence, but by unbelted passengers hitting them.
One last detail: in the event of severe turbulence, your laptop, iPad or phone in front of you can become a real projectile: remember to stow them in the seat pocket in front of you.
About the never-ending fall.
So the aircraft would have fallen 1,800m in 3 minutes at 950 km/h. When you put it that way, it’s impressive, isn’t it? In fact, it’s not at all.
Let’s take things in order, because the media have a knack for turning something totally normal into something exceptional.
No, the aircraft did not fall at 950 km/h! It fell while flying at 950 km/h, which is totally different. A bit like the example of speed bumps, if you take a speed bump at 50 km/h, you’re not going to take off at a vertical speed of 50 km/h! This is its horizontal speed, not its vertical speed, which is the speed of the fall.
Then let’s talk about the 1800m plummet in three minutes. Again, when you put it like that, it’s scary. And if you want to be even more scared, tell yourself that it’s 180,000 cm in three minutes. Well, 1800m in three minutes isn’t a fall, it’s a descent! With all due respect to the media, they could do with checking the facts before writing nonsense.
1800m is 6000 feet, which means a descent of 2000 feet per minute. Well, it’s a totally normal rate of descent when an aircraft leaves cruising altitude and begins its descent.
At the time of writing, passengers on flight AF25 from Los Angeles to Paris are in for the scare of their lives as they plummet at a staggering 2,300 feet per minute. ! And it won’t make tomorrow’s papers, because this is a perfectly normal rate of descent at such altitudes.
Just like this Oslo Paris at 1984 feet per minute. There must be panic in the cabin.
Of course, the closer the aircraft gets to the ground, the slower their rate of descent, reaching rates close to 600 feet per minute on the final leg, a rate that corresponds roughly to a change in flight level at cruise altitude, a figure that will later be used to measure the turbulence encountered during flight.
So this so-called fall is in fact a descent controlled by the pilots, precisely to get out of the turbulence zone, but it comes after the turbulence.
This is clearly shown by the data available on Flightradar24. Here we can see that during the turbulence the aircraft reached a vertical speed of -1500 feet per minute at times.
1500 feet per minute is less than when a plane leaves its cruising altitude!
In fact, there are two distinct periods of fall, which I’ve isolated by enlarging the image to note the start, end and maximum fall speed times.
The first begins at 7:49:43, the maximum falling speed is reached at 7:49:46 and then decreases until the fall ceases at 7:49:49.
The second begins at 7:49:58, with maximum falling speed reached at 7:50:08 and then decreasing until the fall ceases at 7:50:29.
So a 6-second fall followed by a 31-second one, and of course it wasn’t a continuous 1,500 feet per second: each time there was an acceleration, reaching maximum speed and then a deceleration of the fall. Of these 37 seconds, the speed of 1,500 feet per minute was only reached for 3 or 4 seconds.
That’s not to say it wasn’t severe turbulence, the ultimate possible level, and if we’d been in the aircraft I have no doubt we’d have thought the worst, even if, once again, we know the plane is safe and we won’t crash.
But the truth is not a 3-minute infernal fall at an impressive speed lower than that of a normal descent, but an episode of turbulence, extreme though it was, which lasted less than a minute and during which the fall speed of 1500 feet per minute was reached for about 4 seconds.
And if we consider that 700 feet per minute is a “normal” rate of descent for the final phase of a landing, it was only exceeded for 19 seconds.
I’ve shown this by annotating the graph: the red lines represent the start of the fall, the moment of maximum speed and the moment when it stops, and the blue lines represent periods when the fall speed is greater than the rate of descent of a landing.
All you have to do is enlarge the image to clearly read the time scale, and if amateurs like us can do it, I have no doubt that a conscientious journalist can too, just like knowing that a fall of 2,000 feet per minute…is not a fall.
So why so many injured? It’s not the speed of the fall that counts, but the time taken to reach it. A bit like the thrill rides in amusement parks like Disneyland’s Space Mountain: it’s not so much the speed that’s impressive, but the acceleration. When an aircraft descends, it will take some time to reach a descent speed of 2,000 feet per minute. However, when this speed is reached in less than a second, you’re thrown to the ceiling.
Because at no point was the speed of the fall greater than that of an aircraft leaving cruising altitude to begin its descent.
And so, as the graph shows, the fall was not 1800m but around 300 feet, i.e. 90 meters. And 90m in a few seconds is already huge, as evidenced by the passengers’ injuries, so there’s no need to exaggerate.
So rather than talking about a 3-minute fall that didn’t happen, or turbulence where the fall speed was nothing impressive, or a fall of 1800m that was in fact only 90, the media could have reported on the number of Gs endured by passengers during the few seconds of turbulence. But obviously that’s too much to ask of them.
By way of comparison, the infamous flight AF447 reached a vertical speed of -10,000 feet per minute during its stall.
Boeing again
Of course, we haven’t avoided the easy shortcuts and “yet another Boeing involved in an incident”. There’s no denying that Boeing is not going through the most glorious period in its history, but turbulences are not sectarian and hit all aircraft equally hard.
An A350 wouldn’t have fared any better.
Once again, apart from the legitimate fear and panic to which we ourselves would surely have given in, the only dramatic consequences are injury and death, and if the latter is due to a heart attack, the others could have been avoided or greatly reduced by wearing a seatbelt.
What’s more, the 777 is a very safe aircraft which, despite a long career, has only been involved in 4 serious accidents resulting in the loss of the aircraft.
– The crash of Asiana Airlines 214 on landing in San Francisco in 2013.
– The unexplained disappearance of Malaysia Airlines 370 in 2014.
– The destruction of Malaysia Airlines 17 by a missile over Ukraine in 2014.
– The crash of Emirates 521 during a botched landing and late go-around in 2016.
Bottom line
Yes, Singapore Airlines flight 321 encountered severe turbulence which, in addition to causing a legitimate scare, resulted in the injury of 30 people and the death of another. But it’s not so much the speed of the fall that’s the cause as its suddenness.
But all the figures the media have been reporting since the beginning of the affair are false, and what they present as a fall is a controlled descent following the turbulence.
The turbulence caused the aircraft to fall at a speed of 457m/minute, below that of the start of a descent, for a few seconds, and at a speed above that of a final approach for around thirty seconds.
And the fact that it’s a Boeing makes no difference.
Photo : B777 300-ER Singapore Airlines by axell.rf via Shutterstock
Articles similaires
Macbook Pro not allowed on planes: where do we stand?
Air pockets, turbulence: why are we shaken up in flight?
