TACA aircraft crashed in Honduras

[glad rag]

Particularly unpleasant to see U Tube plummeting to the lowest depths.....

[Austrian Simon]

Originally Posted by GobonaStick

I've listened to the ATC, the Spanish transcript sounds correct to me. ... Easy error to make, I guess.

I confirm that, I have listened to the tape myself, with the transcript before me I was able to follow the words and understand them. They are talking about zero two indeed at 23:50 and two zero later at 26:02.

I am just about to correct the translation accordingly.

Servus, Simon

[David K-M]

Mea culpa Simon: the Flight Global article was written to reflect the emergence of the security video rather than to analyse the accident. The low-end 100kt figure, derived in a few minutes, was based on very basic assumptions, and only intended to give a sense of proportion. Having since had the time for a more thorough assessment - from which we've also come up with a speed of 120-130kt - I'll be updating the figure in the story.

Ultimately the question isn't whether the A320 was travelling too fast - the overrun itself settles that - but rather why. Either it was decelerating normally but late, or it couldn't decelerate, or it was deliberately not decelerating.

[Austrian Simon]

Originally Posted by David K-M

Ultimately the question isn't whether the A320 was travelling too fast - the overrun itself settles that - but rather why. Either it was decelerating normally but late, or it couldn't decelerate, or it was deliberately not decelerating.

David,

I think, that question is best answered by the facts derived from flight data recorders and other evidence available, correctly interpreted by the accident investigation team.

Right now we are making an assumption again, namely that the video is not manipulated and the timestamps are correct. I'd certainly concede, that this may be a reasonable assumption, but it remains an assumption nonetheless and is not established fact.

Thanks for jumping in - my respect for your statement!

Servus, Simon

[Robert Campbell]

Video Speed

The speed of the A/C can easily be computed once the frame count per second of the camera is known. The fact that the camera is panning right while the 320 is speeding left in the frames is irrelevant.

If one wanted to give the illusion of increased speed, the frames would have to be free of any stationary objects. Find a stationary object and use it as a reference.

Normal NTSC video runs at 30 frames or 60 fields per second. Surveillance video can run at any frame rate set by the operator.

So, talk to the guy who set the system up first. Then do the math.

[bubbers44]

The first approach was to 20, the second to 02. They decided it was easier to land on 02 with cloud conditions. Either way it is a visual approach over the runway if you go to MAP. You can then land either way if you can stay VMC. Clouds were marginal around 2,000 feet that day so they probably were trying to make it work and found 02 easier to land on. Unfortunately that put them landing downhill on a wet 5400 ft runway with a 10 knot tailwind with a 70 ft cliff at the end. We had strict rules on landing weights and tailwinds so would not have landed. Over 5 knots on a dry runway of tailwind prohibited us from landing.

[Lemurian]

Bubbers,

the first approach was to 20, the second to 02. They decided it was easier to land on 02 with cloud conditions. Either way it is a visual approach over the runway if you go to MAP. You can then land either way if you can stay VMC. Clouds were marginal around 2,000 feet that day so they probably were trying to make it work and found 02 easier to land on. Unfortunately that put them landing downhill on a wet 5400 ft runway with a 10 knot tailwind with a 70 ft cliff at the end. We had strict rules on landing weights and tailwinds so would not have landed. Over 5 knots on a dry runway of tailwind prohibited us from landing.

Sounds fair and safe to me.
A few questions, though :

1/- Were your minima 2700 ft / 3 sm (= 4800 m) ?
If yes, would you have attempted a circling approach on RWY 02 with this METAR :MHTG 301500Z 19004KT 2000S -DZ FEW008 BKN020 OCV080 21/19 Q1016 2KM S SW WSW D/C 8KM PCPN CL HZ ? ( reading it, I have the feeling that all quadrants leading to the final 02 (w, SW, S ) were below vis min and the broken ceiling 700 ft below minimum.

2/- On RWY 02, there is a 5.3° PAPI restricted to A and B cat aircraft. Is that descent path angle a reflection of the actual trajectory you'd find yourself at on short final ?
3/-Corollary : How were speed control and respect of a landing trajectory ?

[bubbers44]

5 km was controlling for initiating the approach. We never could get an answer from FAA or anybody how they report multiple visibilities in different directions and what was controlling. In the US it is prevailing visibility controlling approach legality which means over half of the directions visibility is 5 km. We would have and have in the past initiated the approach with 2,000 broken conditions as long as we had 5 km reported in at least one direction. TGU had certain landmarks they used to determine visibility but they did not have anything to do with prevailing visibility. The cloud bases were not controlling. You just couldn't continue to a landing unless you had the airport visually in sight reaching MDA.

The only time I couldn't land there and ended up at San Pedro Sula the ceiling was 2300 overcast and never saw the ground. Noone landed that day because of the weather. That day they would not allow any 02 approaches to get below 2700 ft AGL. I complained so the next day they notamed all 02 approaches OTS. My complaint was if they publish an approach they should let you perform it.

[bubbers44]

The reason visibility to the s sw was 2 km was that was about as far as you could see with the hills there on a clear day with any clouds hanging around the distant hills. We had no glide angle info for landing. We had reference altitudes crossing some tanks then just maintained about a 1200 fpm descent to flair turning final below 100 ft. Yes we got yelled at sink rate, sink rate a lot from the gpws. Unless you had about a 15 knot headwind to reduce below 1200 fpm descent it usually was going off below 100 ft. We would get fired for doing an approach like that anywhere else but to land in that 700 ft touchdown zone that was required.

[Lemurian]

Bubbers44,

Thanks for all these informations.
I had a feeling that those visibility and ceilings values would somehow have been based on aspect of the local terrain.
Thanks for clearing that out.
The part that is still bothering me is :

We had strict rules on landing weights and tailwinds so would not have landed. Over 5 knots on a dry runway of tailwind prohibited us from landing.

I presume that all operators there would have the same criteria.
Do they ?

[bubbers44]

The 5 knot tailwind was our ops. I don't think Taca had that restriction. We also had a 10 knot max tailwind for all airports we landed at except San Jose, Costa Rica, which was in the valley at 3,000 feet so one day I landed with a 15 knot tailwind there because the clouds were too low to circle but when I got back to Miami with weather coming in with a 13,000 foot runway at sea level the 15 knot tailwind exceeded our ops. We were the only operation limited so sometimes to try to make things safer it just gets more complicated. Of course the reason they changed to 15 knots at Costa Rica was too many flights couldn't circle because of those typical low clouds so flight were diverting.

[NARVAL]

What deceleration rates do Autobrake "low" and "medium" give on an A320 just out of interest (assuming dry runway; typical landing weight) and what sort of ground run distances do these translate to?
You select Max at take-off (if rejected) and it becomes active when ground spoilers are deployed. You use low and medium for landing:
LO waits 4 seconds (!!!) after ground spoilers are deployed and gives 1,7 m/s/s deceleration (5,6 feet/s/s)
MED waits 2 seconds only and gives 3 m/s/s (or 9,8 feet/s/s)
If the antiskid is active (slippery surface) you will not get those deceleration rates.
From experience and without saying it is what should be done, if I felt that even although the computed landing distance for very wet runway was available, the braking might be a serious concern, I would not use the autobrake, but slam both brake pedals "to the floor" as soon as on the ground and let the antiskid do its best with that.You can even brake as hard as you can before touching the ground.You will not block the wheels.

[Flight Safety]

Photogrammetry is quite limited with only a single camera, so I attempted to analyze the Security Camera images frame by frame, measuring the distance the fuselage (and only the fuselage) traveled from frame to frame. Since the aircraft is basically traversing a straight line (down the runway), I used fixed points in both the foreground and background as references. My technique was to draw 2 straight lines (through foreground and background reference points) on the images, one marking the position of the nose of the aircraft on each image, and one marking the position of the nose from the previous image. I could then determine how far the fuselage had moved forward from the previous image.

This technique seemed to work for the first few frames, but then seemed to fail in the later frames as the aircraft's speed begin to skew towards 160 knots in the later frames (161 being the highest I measured). I assumed this might be due to greater pixilation, greater view angles or some other artifacting in the images, as the aircraft got further away from the camera. I also assume there's no way this aircraft could have been accelerating towards 160 knots after touchdown.

The results also seem to indicate that the time stamps on the images are quite accurate.

Some portion of the aircraft is recorded in 9 images. I'm only posting the results for the first 3 measured frames because they are consistent and the following frames start the skewing towards 160 knots.

I used the following formula in Excel to calculate speed. I'm an American so I like to measure in feet

ESN = 1/TD*DTF*3600/FNM

Where:

Assumed Aircraft Length = 123ft 3in
ESN = Estimated speed in knots/hour
TD = Time Difference from previous frame to current frame
DTF = Distance Traveled in Feet
FNM = Feet per Nautical Mile = 6076.1155

Frame 19.828 - First reference frame, marked nose position only
Frame 20.031 - TD = .203 sec, DTF=53.4ft, ESN = 155.9 knots
Frame 20.421 - TD = .390 sec, DTF=102.7ft, ESN = 156.0 knots
Frame 20.828 - TD = .407 sec, DTF = 106.8ft, ESN = 155.5 knots

Again the speeds begin to skew towards 160 knots after this, which can't possibly be right.

Now if someone else knows where the camera is, has access to an accurate scale drawing of the airport (and immediate surroundings), and can reference structures in the background, they should be able to determine where the aircraft was located on the runway in each frame. But I leave this task to someone else.

[Austrian Simon]

Originally Posted by Flight Safety

I attempted to analyze the Security Camera images frame by frame, measuring the distance the fuselage (and only the fuselage) traveled from frame to frame.

Hello, Flight Safety,

thanks a lot for your effort indeed! Great post!

Servus, Simon

[bubbers44]

I calculated a B757 at mglw landing under those conditions and came up with a 155 knot ground speed at touchdown. The camera view is about 2500 ft down the runway so your calculations would show no desceleration.

[TO MEMO]

Caulfield

Try LPHR

frightening!

[CONF iture]

Originally Posted by bubbers44

We had strict rules on landing weights and tailwinds so would not have landed. Over 5 knots on a dry runway of tailwind prohibited us from landing

For planning purpose, I could imagine TACA dispatch had also computed the figures for RWY02 DRY 5kt TAILWIND 62 tonnes giving a Required Landing Distance of 1600 meters (factored distance)
The same figures but for a WET surface would have limited the weight at 58 tonnes.

Crew and ATC look both aware of that 5kt ''limitation'' (?)

TA390 "EH SI SEÑOR. Proceeding directly to the VOR. We request approach to runway 02 and if possible, winds is five knots, landing on runway 02, because there are very low clouds in the circling to 20"

TGU "TACA three niner zero. Confirm you request runway zero two. Winds are at two zero zero with one zero knots. Over"

Once airborne, the crew can eventually discard the factored distance.
RWY02 WET 10kt TAILWIND 62 tonnes giving an Actual Landing Distance of 1400 meters (unfactored distance)
To obey this figure, the crew knows he has, in this especially challenging environment, to proceed to a text book landing and deceleration. It provides only 250 "extra" meters …

But thanks to Simon Dinger and FS effort, I would say that the text book was a lot to put in practice. I could not have used their scientific methods but kept it simple and fully agree with that estimated 130 knots and something. It’s an average speed which means the 320 would probably still be around 140 kt or more when it appears on tape, which could mean a VERY late touchdown … (?)

If it is confirmed that the flaps on the crash site were at a different setting than FULL, I would also opt for PJ2 explanation, even if it’s not an Airbus procedure.
I just hope the guy, in the rush, does not mix the handles … and retract the speed brakes in the same time !?

Vital to some, obviously not to others, taking into account all of the safe operations throughout the world on the Airbus

A final word for Dream Land, I won’t bother you any longer with this stuff in this specific thread after that. There is a multitude of incident reports available dealing directly or not so directly to the Airbus sidestick philosophy, maybe I pay too much attention to them, but maybe you ignore them too much (?)
My personal message and do whatever you like with it: Don’t be surprised one day … to be surprised
Have a safe flight !

[NARVAL]

Of course the reason they changed to 15 knots at Costa Rica was too many flights couldn't circle because of those typical low clouds so flight were diverting.

The maximum tailwind acceptable for the A320 is, to my knowledge, 10 knots. That comes from the Airbus FCOM, and it has been demonstrated and approved. One must remember that it can be with normal flight controls or with the so-called "direct law". The flare on this type of aircraft is a very computed matter with electric flight controls, aside from the increased landing distance due to tailwinds. If a company choses to exceed those limitations with that type of aircraft I do not think Airbus would approve, if asked...After that of course, the captain may decide to do what he thinks best in a difficult situation, but it crtainly should not be allowed on a day to day basis. The A320 is not a 737...

[Lemurian]

Narval,

You don't know what you're talking about, either about the 'Bus flight controls or on the wind limitations.
15 kt is indeed an Airbus-com-DGAC approved tailwind limit used by Air France for airplanes serving the Corsican airports. Enough said on that.
As you wrote, the 737 is no A320.

[alf5071h]

CONF iture Re “To obey this figure, the crew knows he has, in this especially challenging environment, to proceed to a text book landing and deceleration. It provides only 250 "extra" meters …”
If you mean that there is some other approved landing technique which can improve the landing performance then you are mistaken.
A ‘text book’ landing is what should always be aimed for on every landing and it would not require any special tricks; it provides an average ‘performance’ landing. Attempting to land from a low threshold crossing height, landing ‘short’ or at low speed will inevitable break the rules and increase risk.

Re “Once airborne, the crew can eventually discard the factored distance.”
No, why should they. Factored distances are a requirement for good purpose – to maintain the required level of safety – the additions are safety factors not multiples of distance to be traded or ignored.
A wet landing distance (factored or unfactored) is based on ‘standard’ data. There are assumptions about runway friction, which in this instance appear to be much less due to recent heavy rain and/or a ‘slippery’ surface from newly laid asphalt. In addition, landing data takes account of the wind; in a tailwind this is factored by 150%. If wind measurement or assessment is incorrect, or there are sudden wind changes then the data is in error – 150% error; thus tailwind operations have greater risk.

Don’t forget that the speed estimates from the video relate to ground speed; so far there is no public information on either airspeed or wind speed, thus an apparent ‘fast’ landing could be due to either aircraft handling or wind speed.