Tradewinds 747 Wreck in MDE

[Sonny Crockett]

Minus two thrust reversers would be a major factor in going off the end in an 800,000 lb. airplane.....I would be happy to see this be blamed on mechanical issues and not the crew.

Haven't seen CSY Mon on here in a while, hope he wasn't involved.

CSY Mon? Where are you?

 

[ackattacker]

Forgive the ignorant question, but on the turboprop I fly reverse is not allowed to be considered in the takeoff calculations, the theory being that if you abort due to engine failure any reverse would be asymmetrical and hence unusable. Is it different on a 747?

 

[metrodriver]

same for most jets, not sure for the 747, but I assume so

 

[Whistlin' Dan]

Forgive the ignorant question, but on the turboprop I fly reverse is not allowed to be considered in the takeoff calculations, the theory being that if you abort due to engine failure any reverse would be asymmetrical and hence unusable. Is it different on a 747?

It's the same for all transport-category aircraft...the use of reverse thrust is not calculated into the stopping distance, which of course is a factor in determining V1 speed.

However, while take-off perfromance data assumes normal (I.E., "all engines operating") acceleration to V1, many carriers advocate strongly against initiating an abort past 100Kts at heavy weights unless there are definite indications that the aircraft is not capable of flight. In some situations, that creates a "no-mans-land" between 100Kts and V1 in which the "correct" course of action can be nebulous at best.

The bottom line is that if it ends with all the wheels on the concrete, you probably did the right thing. If not, you might have some 'splainin' to do...

Obviously, these guys didn't get it stopped, which leads me to believe that there was either a failure in the braking system, or that for some reason, the abort was called after V1. The failure of a second engine would be one possible reason for calling the late abort.

I still suspect that the seeds for this accident were planted long before the crew showed up for the van.

 

[Draginass]

WD - Speculating, especially publically on a BB, on what the crew did or did not do is counter-productive and not professional at this point. Further, you are not completely correct about reverse thrust not being considering in the takeoff data. On wet runways, the FARs do indeed allow reverse thrust in certification as long as it "is such that exceptional skill is not required to control the airplane" along with some other stipulations. See FAR part 25.109. However, the FAA approved airplane flight manual will contain the specific conditions. What are they on the DC-8? I would assume it's the use of 2 reversers on a wet runway, in addition to some of the other stuff mentioned below. Let us know for sure.

What is productive and enlightening is a discussion of wet runway refusals in general, without comment on what may or may not have specifically happened in Medallin.

Minus two thrust reversers would be a major factor in going off the end in an 800,000 lb. airplane.....I would be happy to see this be blamed on mechanical issues and not the crew.

Haven't seen CSY Mon on here in a while, hope he wasn't involved.

Given the altitude of Medallin and based on Jepps Runway Analysis from Bogota, I would guess (only) that the GW was less than 700k, but could have easily been max gross for the runway limit. Also, civil takeoff data on a wet runway allows a decrease of screen height from 35' to 15' and also allows the use of reverse thrust (if it doesn't require exceptional skill on the part of the pilot). In the case of the 747, wet data allows the decreased screen height (15') and the use of 2 symetrical reversers (presumably since using 3 would require exceptional skill). If the refused takeoff is due to something other than loss of thrust, then 4 reversers can be used as a bonus. The Boeing standard for a "wet" runway (vs. a "cluttered" runway with standing water) is to reduce dry runway V1 by 10 knots.

Why a decrease in screen height and the use of reverse thrust in wet runway certification? . . . . well, as in most things in civil aviation, safety does not reign supreme, money does. If not allowing reverse thrust and keeping the screen height at 35', a huge weight penalty would have to be borne . . . and weight = $$$.

On the DC-10, on how many engines at reverse thrust is the wet runway data based upon? I would assume 1, since the most critical failure would be of a wing engine. However, having never flown the -10, I don't know how much of a control problem is induced with an assymetric wing engine at reverse thrust. I would assume it would be significant, thus disallowing assymetric reverse thrust.

See FAR part 25.109 for general certification requirements for stopping distance.

 

[ackattacker]

Thanks for that, it was enlightening. I suspected something similar, because I have trouble conceiving how a 747 could safely abort using brakes only from V1 on a wet, high altitude runway. I'm not going to add to the speculation, only say that I do hope that the crew is cleared in this one. In my mind the fact that they walked away from it means they did something right, it certainly could have gone much worse.

 

[Junkflyer]

We dialed in some numbers using our companies OPS program for a q-powered 200 in MDE. It gave a max of 753,000 lbs ,but you only get a 256 foot stop margin. Most times your stop margin is 3,000' or better. I wouldn't be at all surprised if they had unknown weight on board coming out of SA. In the old days, they would ask you how much you could carry and that's what their weight and balance would say. The funny thing is all the cargo was already on pallets and nothing was ever added or subtracted.

 

[Draginass]

We dialed in some numbers using our companies OPS program for a q-powered 200 in MDE. It gave a max of 753,000 lbs ,but you only get a 256 foot stop margin. Most times your stop margin is 3,000' or better. I wouldn't be at all surprised if they had unknown weight on board coming out of SA. In the old days, they would ask you how much you could carry and that's what their weight and balance would say. The funny thing is all the cargo was already on pallets and nothing was ever added or subtracted.

Does that data take into account a wet runway, or does it just give you dry runway data and assume the Boeing standard 10 subtraction to V1?

 

[Draginass]

Posted in error.

 

[heilhaavir]

Does anybody know if there was an engine intermix on that airplane?