Report from Flightglobal: https://www.flightglobal.com/airlines/v ... 22.article

One of Vietjet Air’s Airbus A321s has apparently suffered structural damage after a hard landing at Dong Hoi Airport (VDH) in central Vietnam.
FlightGlobal understands that the accident occurred in the early evening on 16 October as the aircraft, VN-A639, landed on a wet runway in VDH after operating flight VJ260 from Ho Chi Minh City (SGN).

Flight load data supplied to FlightGlobal indicates that the vertical force during the landing was 4.27g.
It also indicates that the landing, on runway 29, took place in a 90° crosswind of 23kt from the right, gusting to 33kt.

VJ's comment:

The aircraft was operating with passengers and flight crew as scheduled and all onboard disembarked normally. The airline is checking the aircraft’s overall status under Airbus’s instructions. The bad weather in central Vietnam has also impacted this process.

Perforations on the fuselage:


Nosewheels:


Base on fr24.com, this was just the aircraft's second flight after months of sleeping in the storage.
Flight's link on fr24, flying SGN-VDH: https://www.flightradar24.com/data/airc ... 9#25c984ff

Airframe's info:

planespotters.net


How do you think about this incident?
This incident had made the VJ's A321's troubles list, as the type had many significant incidents in the last few years. An A321neo losing nosewheels while landing in BMV, an A321ceo skidded off the runway in SGN.

Considering the reported weather they could have been caught out in the final moments. Maybe we have a few A321 drivers on here who can comment on the crosswind component gusting up to 33 knots. I don't think it's at it's maximum but it is up there. Hard to tell much more at this point. Investigators will surely pull the recorders and see if human factors have played a role.

9MMPQ wrote:

Considering the reported weather they could have been caught out in the final moments. Maybe we have a few A321 drivers on here who can comment on the crosswind component gusting up to 33 knots. I don't think it's at it's maximum but it is up there. Hard to tell much more at this point. Investigators will surely pull the recorders and see if human factors have played a role.

Max Crosswind demonstrated is 38 kts for the A320 family, gust included. That’s a Certification limitation, so the company can always be more restrictive. Also, if the runway is wet or contaminated that number can go down.
It is very difficult to make an early assessment without more information, but to land that hard I would suspect windshear or downdraft on the very last seconds before touchdown. The damage to the nose wheels and front fuselage make me suspect of a “nose first” landing.
As a former A320 driver, I found that in 90º crosswind and especially with sharklets, roll control could be a bit difficult but manageable. Let’s wait for more info.

A lot of pilots out there who aren’t getting much flying. Don’t forget about that. After the PIA debacle, plenty of pilots I know didn’t roll their eyes at what happened, with months sitting at home getting rusty, they said, there but for the grace of god go I

9MMPQ wrote:

Considering the reported weather they could have been caught out in the final moments.

I've never really understood this excuse. From day one of your private pilot training you are taught to use good judgement and that you are responsible for the safety of the occupants and the aircraft. The pilots knew the winds and that the direction and speed can change without warning. They proceeded to land anyway. They had other options at their disposal to ensure a safe and stable landing.

Antaras wrote:

Flight load data supplied to FlightGlobal indicates that the vertical force during the landing was 4.27g.

What's the average and certified vertical force range?

SIVB wrote:

Max Crosswind demonstrated is 38 kts for the A320 family, gust included. That’s a Certification limitation, so the company can always be more restrictive. Also, if the runway is wet or contaminated that number can go down.

The maximum crosswind vs runway condition is in FCOM-LIM

ABpositive wrote:

Antaras wrote:

Flight load data supplied to FlightGlobal indicates that the vertical force during the landing was 4.27g.

What's the average and certified vertical force range?

Haven’t got my Airbus manuals with me at the moment but you start talking to airbus for whats classified as severe hard landing at around VRTA of 2.8g on a 320, someone might refine that for me. So this one is well above that at 4.27g.

Plus there is also RALR rad alt rate as well to consider.

The gears are the first parts to start needing replacement parts. But this one is way more.

My thoughts is that this was a very hard bounced landing followed by nose first on second contact.

787SIN wrote:

My thoughts is that this was a very hard bounced landing followed by nose first on second contact.

I agree, it seems this could be the case.

zeke wrote:

SIVB wrote:

Max Crosswind demonstrated is 38 kts for the A320 family, gust included. That’s a Certification limitation, so the company can always be more restrictive. Also, if the runway is wet or contaminated that number can go down.

The maximum crosswind vs runway condition is in FCOM-LIM

Yes I’m aware of that, I don’t have my FCOMs anymore as I changed fleets. The point is that 33 kts gust is approaching the certification limit, not unflyable but challenging. Very hard to make a judgement without being there.
A fair point that someone mentioned before (cedarjet), most pilots are flying much less..

TTailedTiger wrote:

9MMPQ wrote:

Considering the reported weather they could have been caught out in the final moments.

I've never really understood this excuse. From day one of your private pilot training you are taught to use good judgement and that you are responsible for the safety of the occupants and the aircraft. The pilots knew the winds and that the direction and speed can change without warning. They proceeded to land anyway. They had other options at their disposal to ensure a safe and stable landing.

And even then conditions can still rapidly change and catch up with you. Think sudden extra high gust of wind or windshear at the last possible moment. I'm just keeping an open mind. We certainly don't have much to go on so let's see what investigators find.

Antaras wrote:

How do you think about this incident?

It'll buff out...

All kidding aside, I think it's safe to say we've seen worse before.

It'll be interesting to see how long it takes this aircraft to RTS.

Why don’t we wait for the official report instead of speculations and making assumptions

777luver wrote:

Why don’t we wait for the official report instead of speculations and making assumptions

VJ paid the media so well that I couldn't find a single Vietnamese article writing about this incident even though it happened a week ago. I couldn't find anything on Vietnamese CAA either, even though the CAAV supposed to report every single incident/accident happened in Vietnam.

Everything we have is, sadly, just a nice English article from Flightglobal, an official reply from VJ quoted by Flightglobal, as well as some single reports on other English sites.

I am expecting no "official report" from the authorities or anything else. This incident is theoretically not existing in Vietnam.

The airline probably did not want to pay for a diversion, so they took the risk.

Where would the sensor for that g figure be located?

Nomadd wrote:

Where would the sensor for that g figure be located?

Well, you can easily calculate it by the aircraft's landing weight, the touchdown vertical & horizontal speed, the touchdown angle...
Or you just need to check the black box. Yes, I believe that there are some kinds of g-sensors installed on the airframes. or at least there are some kinds of system which calculate the landing-g by the above figures.

Ziyulu wrote:

The airline probably did not want to pay for a diversion, so they took the risk.

Perhaps.
According to the location and the weather, it would be an expensive diversion

http://www.gcmap.com/mapui?P=sgn-vdh,da ... ph,vdh-han

Base on the map:
HUI and DAD (not more than 150 miles from VDH) were closed due to the storm last week.
THD and VII (not more than 180 miles from VDH) were closed as they were affected by the flood.
So the nearest solution is a diversion to HPH (239 mi) and HAN (260 mi), and obviously, those diversions would be so expensive for an ULCC. Moreover, I heard that the aircraft was already making a few turnarounds and drawing many circles in the sky before the hard landing, so there might be not enough fuel to continue flying to the two northern airports, leaving VDH as the only solution.

Anybody know how this translates into vertical speed at touchdown / fpm?

Nomadd wrote:

Where would the sensor for that g figure be located?

Located near the CofG. The VRTA parameter comes from the DFDR accelerometer, which is found under a cabin floor panel.

pnutt wrote:

Anybody know how this translates into vertical speed at touchdown / fpm?

No info.
The flight lost its trace on both Fr24 and FlightAware around 30 minutes before the touchdown.

pnutt wrote:

Anybody know how this translates into vertical speed at touchdown / fpm?

Gravity is 9.8m/s.
Times that by 4.27 = 41.8m/s
Times that by 60 = 2510.7m/min
Converted to ft/min = ~8237ft/min

Someone check my math, but that sound like an owie.

n797mx wrote:

pnutt wrote:

Anybody know how this translates into vertical speed at touchdown / fpm?

Gravity is 9.8m/s.
Times that by 4.27 = 41.8m/s
Times that by 60 = 2510.7m/min
Converted to ft/min = ~8237ft/min

Someone check my math, but that sound like an owie.

Your converting acceleration in to speed. So wouldn’t be correct. Gravity is 9.8m/s2, two being a small two.

If they hit at 8,000ft/min we wouldn’t just be seeing some sheared tie bolts on the nose wheel(s) and a bit of skin deformation at Frame 20.

Rad alt rate RALR would have been being measured too by the aircraft systems and available on the hard landing report (report 15) through the ACMS. Plus also on QAR/DFDR.

FluidFlow wrote:

n797mx wrote:

pnutt wrote:

Anybody know how this translates into vertical speed at touchdown / fpm?

Gravity is 9.8m/s.
Times that by 4.27 = 41.8m/s
Times that by 60 = 2510.7m/min
Converted to ft/min = ~8237ft/min

Someone check my math, but that sound like an owie.

Thats bot how acceleration works. The units are m/s^2.

Landing with 41m/s vertical speed would cause way more than an owie. Thats like parking into your garage with over 120km/h. Not a good choice...

Ah, crap. I knew that sounded outrageous. Disregard...

787SIN wrote:

n797mx wrote:

pnutt wrote:

Anybody know how this translates into vertical speed at touchdown / fpm?

Gravity is 9.8m/s.
Times that by 4.27 = 41.8m/s
Times that by 60 = 2510.7m/min
Converted to ft/min = ~8237ft/min

Someone check my math, but that sound like an owie.

Your converting acceleration in to speed. So wouldn’t be correct. Gravity is 9.8m/s2, two being a small two.

Acceleration can be converted to speed - if an object is moving in a downward motion and experiences an upward force that results in 0 velocity, and you know both the time that the force was experienced and the actual force, you can calculate the initial speed.

The challenge of course is identifying the duration and actual force.

Let's assume that the stated acceleration (4.27g) is a peak value, and that the average value was only half that.
Let's also assume that the time from initial ground contact to the point where the descent rate was 0 is 0.8 seconds.
Let's also assume that the aircraft did not bounce.
And let's ignore the fact that different parts of the aircraft (nose vs mains) probably contacted the runway at different times for different durations and experienced different forces....

So we have a force of (4.27 * 9.8m/s2) / 2 applied over 0.8 seconds resulting in a velocity of 0.

In that scenario, the end result is 16.73m/s = 1003.8 m/min = 3293 ft/min. That value assumes that the aircraft DOES NOT bounce. Any climb rate achieved by a bounce has to be subtracted from this calculated sink rate. So, if for example, it bounced and resumed flying with a rate of climb of 500 ft/min at the instant moment it left the ground, then the sink rate at landing would have been 2793 ft/min.

Without knowing if it bounced (and what it's vertical speed was the moment it left contact with the runway), and without knowing the actual amount of time it spent in contact with the runway, or the average acceleration over the entire time it was in contact with the runway, we're just guessing; but I would guess the above numbers are within an order of magnitude of being correct.

An interesting data point. The NTSB report on N980DC (the DC-9 which landed hard and lost the tail in 1980 on a test flight) states the following:

"Based on INS vertical speed data, at main gear touchdown, the sinkrate was about 16.2 fps. The main gear became airborne about 0.5 seconds after touchdown; 0.2 seconds later the nose gear touched down, and 0.4 seconds after the nose gear touched down the main gear touched down again. The sink rate at touchdown exceeded the aircraft's ultimate vertical speed limitation for landing (12.25 fps) and initiated failures at the fuselage locations described in this report."

https://www.ntsb.gov/investigations/Acc ... AR8202.pdf

So in that case, the DC-9 landed with a sink rate of 972 ft/min resulting in structural failure.

If I remember correctly, some of FX MD11 crashes mentioned 10 fps as design limit and 13-14 fps leading to a crash. It has to do with energy absorbtion by MLG struts, once they are at the travel limit, further slowdown is by the structure, and acceleration goes up pretty fast with small velocity change. Basically it is an impact after that.
10 fps is, using backside of envelope computer, is about 3 deg descent with no flare. I suspect any airliner would need to be close to that number for design limit.