Airbus 320 Question about dual engine failure and gliding

[Premium]

BTW....Green dot or best L/D decreases with both altitude and weight

This statement is a bit misleading....
The best L/D ratio does not change depending on weight....however the speed necessary to achieve it does.

[HavaJava]

Sorry A330 but you're still saying the same thing as before (which we are still not arguing about) but not giving a real answer to the question. The only question is why Airbus says 2.7 nm/1000' @ 280 kts and 2.5 nm/1000' @ GD. So far Toga gave the best explanation, but it would be interesting to have an aerospace engineer confirm it.

[ca787546]

I'm in South America by the way I still think the best answer so far comes from TOGA Descent, drunk and all in Asia
Well, the thing is that they should specify something along the lines of "the glide ratios below for optimum relight speed are calculated if such speed is maintained until..." Plus you don't know at what altitude you're suffering a dual engine failure. I understand what A330 is trying to say. He says that the priority is to get at least one engine started. Now, I believe he understands my question as well, which is that all I want to know is why the QRH says that green dot gives me 2.5nm/1000ft and 280 kts gives me 2.7nm/1000ft. There is no specification as why or what it is based on. That is why the best answer so far is TOGA descent's, which basicly says that once you have the altitude to use APU bleed and therefore try a starter-assisted relight you will switch to green dot, and that's the way you'll do it every time. In that case, the higher groundspeed of flying 280kts above FL250 will give you a high glideratio. I am JUST GUESSING HERE, but I am thinking that maybe the 2.5nm/1000ft is an average throughout different altitudes and therefore GD speed at the altitudes at which the optimum relight speed glide ratio is being considered would actually be higher than 2.7nm/1000ft, but since it is not considered for the QRH procedure to fly GD at those altitudes, then it isn't being taken into consideration for the average of GD glide ratio.
Now, I'm tired, and if I read what I just wrote, it probably would just not make sense, so, I'll apologize in advance, lol.
Cheers,
DNB

PS: Basicly, using fictituous numbers, I'm saying the QRH considers you'll fly at 280kts until FL200 (max alt for engine start ith APU when speed is above 150kts) and then start the APU and deselerate to GD. Thus the glide ratio for 280kts is considering you'll fly it until FL200, and the GD glide ratio considers you'll fly it from FL200 to the ground and configuring at 3000 feet. Now, here's the pickle, if that is the actual answer, they should consider that you may maintain 280kts farther in case you were dispatched with an Inop APU. I know it's crazy, but heck, it could happen.

[ahramin]

It could always happen. How many times have airbus cockpits lost all screens? And don't forget that 757 that was dispatched with one gen inop, then lost the second gen, the apu, and the windmill, all for unrelated reasons.

[TOGA Descent]

Okay. Slept that one off.

The QRH is misleading as it wants you to start an engine, not glide to the ground. If you maintain 280 kts, after a dual engine failure, you will not glide as far as if you slowed to green dot.

You haven't been paying attention. Airbus designed the QRH around "Assumptions". One of those assumptions being that you will re-start both engines following a dual failure.

Or, as ca787546 stated, that at some point you will shift gears (Start APU, etc) and then at green dot if can't get one started.

The QRH is not misleading, it is simply dealing with two different issues, and therefore, it makes different assumptions regarding each.

[TOGA Descent]

I’m going to try to explain this philosophy of “Assumptions” used in Airbus manuals and documents.

As most of you know, when an abnormal situation occurs in the Airbus, the flow of procedures is typically a logical sequence of events, and is part of the training found in the FCTM (Flight Crew Training Manual), another assumptive document.

The FCTM doesn’t teach you HOW to fly; it teaches you how to fly THIS Airbus. The FCTM “Assumes” that you have already mastered the basics of flight (Admittedly, Boeing and other manufactures, do the same with their FTCM documents, however, I am trying to make a point).

Following, are two examples of “Assumptions” made in various Airbus manuals.

First example. During flight we get this ECAM, “ANTI ICE CAPT TAT ‘FAULT’ ”

ECAM displayed the problem, but does not indicate any required procedures.
You refer to the QRH, then,
You refer to the FCOM.

Pilots using some common since (Most of us here) would then Refer to the MEL and find that the aircraft cannot be dispatched with this fault (Depends on your MEL program). We are cruising towards an airport in Nepal, where there is limited maintenance and no spare parts inventory. Divert? Absolutely! Or, our destination happens to be Bangkok. Continue? No reason not to. Full maintenance support and a good spare parts inventory available

You can see that all the way along, assumptions were made that we would do various things, and would do them in a logical order.

Second Example. Open a generic Airbus FCOM volume 3; refer to section 2.70 (Power plant) and show me the section that deals with ENGINE FIRE. You won’t find it!

Assumptions seem to be, that after the ECAM procedures are completed, that the fire is out, and you are simply dealing with an engine that has been shut down.

This is another EXAMPLE of the "assumption" Philosophy that Airbus uses, just like the assumptions made with the differences between restarting after a dual engine failure, and gliding at green dot, ;and various other issues.

[TOGA Descent]

It could always happen. How many times have airbus cockpits lost all screens? And don't forget that 757 that was dispatched with one gen inop, then lost the second gen, the apu, and the windmill, all for unrelated reasons.

I recall, twice. And, both times the pilots caused it by not correctly applying an MEL procedure prior to departure.

I'm going from vague recollection, but the story is something like this....

On one occasion, the crew departed with DMC-2 MEL'ed "inop". They selected DMC F/O on the switching panel, but they didn't complete the related MEL Operational Requirements. During flight, AC bus 1 failed. The entire cockpit went black. It was several minutes until they noticed a single light on the overhead panel. "AC ESS FEED" Fault. They push that button, powered the AC ESS bus from the AC2 bus, and everything came back to life.

The MEL procedure called for them to select that button (AC ESS FEED), prior to departure.

[ca787546]

Once again, I agree with TOGA Descent.... EXCEPT! There is an engine fire procedure in FCOM 3.02.26 P2 and P3. It is a bit misleading because one would expect it to be under ATA number 70, but since it has to do with Fire Protection it is at 26.
Regards,
DNB

[TOGA Descent]

Once again, I agree with TOGA Descent.... EXCEPT! There is an engine fire procedure in FCOM 3.02.26 P2 and P3. It is a bit misleading because one would expect it to be under ATA number 70, but since it has to do with Fire Protection it is at 26.
Regards,
DNB

You are absolutely correct. You just saved me from the greatest of the pilot sins. I got caught up in the problem (Trying to explain “Assumptions), and lost site of the situation.

It's true that it exists in 3.02.26 - but as you stated - it is misleading. It's along the same lines as putting the procedure for a total electrical failure, in 3.02.34 (Navigation) - ADR 1 + 2 +3 Fault, or IR 1 +2 +3 Fault!


Nonetheless, it's interesting, that 3.02.26 finally points you to 3.02.70, Engine Shutdown.

We should write a book. "Learning to Speak Airbus", the worlds 6,913th known living language!

[A330]

Second Example. Open a generic Airbus FCOM volume 3; refer to section 2.70 (Power plant) and show me the section that deals with ENGINE FIRE. You won’t find it!

Assumptions are, that after the ECAM procedures are completed, that the fire is out, and you are simply dealing with an engine that has been shut down.

This is another EXAMPLE of the "assumption" Philosophy that Airbus uses, just like the assumptions made with the differences between restarting after a dual engine failure, and gliding at green dot, ;and various other issues.


This is completely absurb and this thread is now a concern.



Posted: Wed Jun 07, 2006 6:17 pm Post subject:

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Okay. Slept that one off.

A330 wrote:
The QRH is misleading as it wants you to start an engine, not glide to the ground. If you maintain 280 kts, after a dual engine failure, you will not glide as far as if you slowed to green dot.


You haven't been paying attention. Airbus designed the QRH around "Assumptions". One of those assumptions being that you will re-start both engines following a dual failure.

Or, as ca787546 stated, that at some point you will shift gears (Start APU, etc) and then at green dot if can't get one started.

The QRH is not misleading, it is simply dealing with two different issues, and therefore, it makes different assumptions regarding each.


That is exactly what I was saying, and the QRH is misleading in that the 280kts glide distance versus green dot is false. Green dot will give you better glide performance everytime.

I think that Asian beer has too much MSG...would that be Tiger or Singh perhaps?

[TOGA Descent]

This is completely absurb and this thread is now a concern.

Did you pay attention to the fact that I was corrected, and acknowledged my inaccurate statement, then clarrified my comments?

Furthermore, if you read carefully, you'd see that I used terms such as; "Seems to be"; "EXAMPLE", "Assumed", "etc". I think that http://www.dictionary.msn.com could help with these terms.

Since we're human, we all make mistakes. Admitting that we've made one is not so difficult.

Now, a rhetorical question. I'm curious, as an A330 Captain, is this how you demonstrate good CRM practices to your crewmembers? ("completely absurb...", "now a concern...", etc)

That is exactly what I was saying, and the QRH is misleading in that the 280kts glide distance versus green dot is false. Green dot will give you better glide performance everytime.

I think that Asian beer has too much MSG...would that be Tiger or Singh perhaps?

Nobody is disputing that. The point is that they are different, because Airbus has determined them to be 2 different events, thus have assumed that two different things would be done, so the corresponding outscomes - Glide Ratios (GR) - would also be different.

Also, don't loose track of the assumption that one GR is assumed to a straight-line distance to the ground, and the other is as straight-line distance to the 3000 feet level.

Tiger. And, I need more!!!!

[A330]

I am normally very pleasant, especially after a few tigers...

Some of the info and responses on this site can be frustrating with many wannabes and clueless guessers. I do enjoy reading the odd thread and responding and enjoying some good entertainment.

Sorry about the backlash.....I'm on my third Corona, and feel much better.

[TOGA Descent]

I am normally very pleasant, especially after a few tigers...

Some of the info and responses on this site can be frustrating with many wannabes and clueless guessers. I do enjoy reading the odd thread and responding and enjoying some good entertainment.

Sorry about the backlash.....I'm on my third Corona, and feel much better.

Well, I've been mixing Tiger and JD, so I too should appologize, if I could remember the meaning of the word. Jeeez. Took me 10 minutes to write this....

Time for sleep....

[Surfinsight]

Hi Guys !

I've read all this topic with a great interest. I don't know if it came from this forul or others discuqsion, byt you question to me seems fair and muqt have brought question to airbus, because i learned to fly the A320 last year and remembered differznt ratio given in the FCOM.so now in 2016, I'm glad to inform you that it finally make aerodynamical sense, ratio given for 280 or 300 knots is 2NM/1000FT and at green dot 2,5NM/1000FT.

So after maximum 10 years, you all can fk ally rest on your backs.

Cheers from cataluna

[Panama Jack]

The simple answer to your question: "Airbooooooz Logique".

[cncpc]

As for Piche and Yeager, i think they were too busy crapping themselves.

What do you base that on?

[photofly]

The GD ratio is 2.5nm/1000ft, while the 280 kts range with 70Tons(154Klbs) is 2.7nm/1000ft.... How is this possible, considering that GD is the best L/D speed and GD is below 280kts when flying at 70Tons?

It isn't possible, and one of those figures is wrong. If you can get 2.7nm/1000ft at one weight you should be able to get it at any weight, by gliding at an appropriate speed.

edit: didn't see that it was such an old thread, but glad the question was resolved.

[AuxBatOn]

Aircraft configuration could be different (RAT or not, windmilling or not, etc). But photofly is right, for a given speed and configuration, glide ratios remain constant, regardless of weight.

Having said that, I only browed through the posts and this may have been answered...

I also wanted to correct a poster that said drag is not influenced by weight. Induced drag is influenced by weight.