TACA aircraft crashed in Honduras

[Lemurian]

Bubbers44,

Here is the FCOM extract :

"LDA = Landing distance available : 1650 m

Baseline calculation : LW = 60 T ; RWY wet ; 5 kt tailwind : 1,352 m
(1110m + 10% altitude correction, 10.5% tailwind correction and -3% for operating reversers ).
According to these figures, the aircraft dispatch was legal.

Now I calculated the maximum allowable weight in these conditions and I found 68 T, quite a hefty margin, it seems.

It is now time to look into the influence of the 10 kt tailwind : a whopping 21 % ! and in this case a landing weight of 66 t was allowed.

Our landing distance at 60 t and 10 kt tailwind now comes to 1,472 m"
There is no correction for runway slope (which really surprised me ! ).

But now, out of the QRH, this is the in Flight performance for required runway length. still at 60T:
"In-Flight performance tables,
Considering an airport elevation of 3,300 ft and a wet runway. And a landing weight of 60 tons.
Base line : Landing runway length required : 1640 m
to which the following corrections apply :
Altitude : 3% per 1000 ft ---> 10%
Tailwind : 21%
Operating reversers : - 8%
Vapp = Vls : - 3%

Total correction : 20% ---> 328 m

So the *required runway length* for these conditions is 1640 + 328 = 1,968 m


Touch-down speed
Still from the tables and at LW = 60,000 kg...---> 130 kt which translates into a 140 kt TAS or 258 km/hr a ten knot tailwind makes it a groundspeed of 276 km/h.


Approach conditions :
Weather conditions : Ceiling (broken) reported at 2,000 ft over the field, few clouds as low as 6 to 800 ft.
Visibility is 2,000 m, which is regarded as poor.
Wind is 190° at ten knots, straight down runway 02.
The *circling* approach on 02 consists on a descent on the Runway 19 VOR approach, gear and flaps down (config 2 or full depending on airline SOP) down to 6,000 ft, then then open some 45° right in order to join the visual circuit for RWY 02 west of the airport.
The least we could say is that the *circling* (equivalent Spanish is "circular" ) conditions at that moment were marginal, both in terms of visibility and ceiling.


Approach visual geometry from the cockpit : Info from both the videos available on the net and some thoughts from pilots with experience on TGU :
They will give you a pretty good idea of a tunnel vision in low visibility . One thing is doing this approach in CAVOK conditions when a general vista of the relief and the landscape is given to you, another is just being able - and concentrating on - seeing just about 20 seconds worth of flight in front of you. The notion of horizontal and vertical become rather academic and even more so when your final path follows a downward slope toward the runway. The tendency to be high is fierce.


Some picture interpretation
The speed at which the airplane came to the road and the embankment, especially considering that it had first to drop some 20 m down that cliff at the end of the runway shouldn't have been very high. The TAM 320 was completely destroyed at an estimated ground speed of 90 kt.
The port smoking brakes seem to bear the indications of some wheel braking (did it start the fire we see in the first video ? )


Some aspects of FH
That crew was very aware of the conditions and the initial decision to try for Runway 02 had the wind been less than 10 kt is reasonable. Some twenty minutes later, a 10 kt tailwind becomes acceptable but they were at that time beginning to pile the odds against them. My question is " Why ?". On the ATC tape, the pilot sounded very sure and sharp."

Your thoughts, now Bubbers !