Jet aircraft descents

[newmei]

Just a brief question....Doing a report on a aicraft accident. Keeping in mind that there was no other traffic involved and the aircraft was in mountainous terrain what is a "normal" descent rate for a jet aircraft under 10000 ? Is it normal for a jet to be 6000 agl 35 miles from the landing airport? That seems kinda low, or am I missing something?

 

[flyhard]

The question of low is relative. In the perfect three to one decent world, 6k is a little low. The thing to remember in most jets decending and slowing cannot be accomplished at the same time. It also depends on what atc does with you. Some airports are notorious for the slam dunk approaches, meaning that they keep you high as long as they can. So I guess the answer to your question really depends on the situation. Me personally, I like to be a little on the low side when planning a decent, that way is you do get a speed reduction you can still make your target altitude.

 

[FSB99]

the above post is pretty thorough. i'd just add (reinforce) something he said. the altitude is relative, and without knowing what the mea, msa, or off route min altitudes are in the area the subject airplane was flying, it'd be hard to say that 6000 feet 35 miles from the airport is too low. usually, atc gives you the altitudes, and except for radar vectoring on an approach, they altitudes assigned are usually higher than the published minimum altitudes. now, when you get into areas where atc/radar coverage is minimal, i.e, mexico, south america, some parts of the rockies, it's critical for the flight crews to review and know what those published minimum altitudes are.

some times in the new york area, they'll descend you really low, pretty far from the airport.. 6000 feet 35 miles from newark isn't abnormal. then again, there aren't any 6000 foot peaks in that area, either.

and to somewhat answer your question of descent rate below 10,000 feet, again, like the above post said, most jets have a hard time going down and slowing down at the same time. it kind of falls in line with personal preference and technique, as well as what the company's training standardization has to say. personally, i don't follow one way or the other every time, you have to be able to adapt to the specific situation. if i know there's no speed restriction, i'll keep the airplane at 230 or 240 below 10,000 feet. depending on how far i need to go down and how long i've got to do that, translates into the descent rate..
the airplane i fly will do at most 1800 feet per minute, clean, at 230. with some flaps out, you can get that over 2000 fpm. but for comfort sake, below 10,000 feet, what i've seen at my airline is generally no more than 1500 fpm below 10,000 (again, subject to the specific situation.)

good luck on the report, hope this gives some insight.

 

[avbug]

Altitude and descent rate are two different things. The former is where you are, and the latte is what you're doing.

It's not uncommon to be brought to a lower altitude in a terminal area. There is simply not enough information to answer the question.

Was it a vector? Was it part of an enroute structure? What type of operation? Was it mountainous terrain, and was it in compliance with minimum safe and terrain obstruction altitudes? Was it at or above the minimum vectoring altitude if being vectored? What was the purpose of being there?

Is it common to be that low that far from the airport? Sure. Also not. What are the circumstances?

And what does that have to do with rate of descent?

 

[trainerjet]

or am I missing something?

WE are missing something. We are missing WAY too much information to make any educated statement regarding the facts of this incident.

I fly aircraft in mountainous terrain on a daily basis, and one thing I can say for sure is that there is no such thing as "normal".

 

[F70pilot]

I always shoot for an altitude of 10,000 feet and an airspeed of 250 knots by thirty miles from the destination if possible.

 

[newmei]

The report is on the Cali, American Airlines crash. Reading the report it just struck me odd that at 38 (something) miles out they'd be 6000 feet above the airport. They were at 9000 ft when they hit the mountain, and the airport was at 3000 feet. Obviously not the direct cause of the crash, (probably not even a FACTOR) nor do I have any place as a accident investigator, however it seems that if they were doing a standard descent that they'd stay higher. However, it was in a non-radar enviroment with many other factors. A standard descent is what in a jet? 1500-2000 fpm or so? I calculated that even at 250 kts which they would'nt maintain all the way to the airport that they'd only have to descend at 750 fpm do get to the airport on target, seems a little shallow to me.

 

[trainerjet]

There were MANY factors that led to this accident (as there are many factors that lead to virtually ALL accidents). Not the least of which was their situational awareness. They were unsure (or mistaken) of thier positon, and therefore all of your speculation on "normal" descent rates and proper altitudes at certain distances from the airport do not apply here, because they thought they were one place, when they were in fact, someplace else.

Then, there were all the other factors which, when added together, led to this accident.

Since you were interested enough to read this report in the first place, go back and read it again, and maybe again. There is much to be gained from the full understanding of all the factors which led to this accident.

 

[FSB99]

keep researching. i've never been to cali, don't know anything about that airport. however, if you look up the approaches available there, could they perhaps be somewhat labor-intensive? meaning, maybe a dme arc with various descent points along the way? if they were planning for a lot of work through the approach, perhaps they got down quickly so they could slow down, get configured early, so they could focus on the approach at hand, without having to worry about slowing and configuring during the approach itself.

but then again, what the hell do i know.. hasn't this accident been investigated throroughly by the professionals, and written statements been published about it? if so, maybe look into seeing what has been written about it already.. may give you the answers to the specific questions you're looking for.

but again, regarding descent rate.. there really is no solid answer for you. it varies day to day, hour to hour, airplane to airplane, etc. your question on its own is almost like asking a cfi, "how many degrees of rudder should you apply during a crosswind landing." too many variables to give a solid, direct answer.

 

[newmei]

Yes, many factors here.....like I said I was'nt trying to play accident investigator. Just thought it was unusual thats all.

To my knowledge it was a straight in arrival. The major factor though was slight disorientation which in itself was was'nt the killer. The incorrect programming was that caused a turn towards terrain that was higher and then a turn back to course which was into even higher terrain. Then there was the spoilers that stayed up during the evasive climb. I guess the comforting thing is that there are many factors (chains) in a accident, but the sad thing is it can be just that one slight factor that completes the chain. Should be a interesting report.

Thanks guys

 

[T-Gates]

A friend of mine at Eastern who flew into Cali for years said that the Braniff guys (who sold the routes to EAL) always tought them to never accept the straight in approach, and to always do the full procedure. When EAL sold the routes to AA, the EAL guys passed on the same information... He said that Cali was a great layover back in the day and that alot of guys got in real trouble trying to shave off precious minutes getting in there.

Alot of CFIT accidents result in not following the procedure on the plate.....

But Trainerjet is right, altitude alone was not the only factor....

They had the wrong fix in the FMS.....(Jeppesen's Fault) and they tried AA's escape manuver with flight spoilers still extended....

But blame cannot be solely placed on the pilots.

 

[flx757]

I guess the comforting thing is that there are many factors (chains) in a accident, but the sad thing is it can be just that one slight factor that completes the chain.

You are correct about the chain of events which leads to most accidents. My wife is a former NTSB Air Safety Investigator (she made a very, very difficult decision to leave this important and satisfying positon to pusue her dream of being a pilot...and she's doing quite well with that, I'm pleased to say), but we have spent many hours discussing various accidents and the chain of events which lead to these accidents. And how there are always several chances along this chain in which to break the chain. Then there is the final opportunity in which to break the chain.

In this particular accident, the final opportunity to break the chain was lost when the crew did not retract the speedbrakes, but that was only one of the many links in this chain. And as T-Gates pointed out, and the NTSB concurred, this accident was not solely the fault of the pilots.

 

[Iceman21]

Where can I get specific info on this accident? I have been scouring google for about an hour and the best thing I have come up with is the CVR recording transcript.

That CVR recording has perked my ear and now I wanna research it some more.

Thanks

 

[DitchDriver]

Wally Roberts used to have some good info about that accident. It has been taken down from his stite:

www.terps.com
www.wallyroberts.com/consultant/


For some more Cali stuff, look in

www.bluecoat.org/reports/ACF_97-1_Minutes.pdf
www.avweb.com/other/avma0001.html

 

[flx757]

Where can I get specific info on this accident?

Even though this was a US registered aircraft operated by a US airline, the accident occurred in a foreign country, and therefore the accident investigation was under the jurisdiction of the agency of that country. The NTSB was present only to provide assistance. You can request information from the NTSB at

490 L'Enfant Plaza, SW
Washington, DC 20594
(800) 877-6799 or (202) 314-6551

and refer to NTSB Identification: DCA96RA020 . The docket is stored in the (offline) NTSB Imaging System. There is also an online request form available here where you can request information under the Freedom of Information Act (FOIA).

Or you can request information from the Aeronautica Civil at Avenida El Dorado No. 106-95, Santafe' de Bogota', D.C., Colombia.

Unfortunately, often information on accidents occurring outside the US is sometimes difficult to get your hands on and requires a little time and effort. But is often well worth it.