Airbus 320 Question about dual engine failure and gliding

A330 · Post by **A330** » Tue Jun 06, 2006 10:59 am

Flying at 280kts, what are you trying to do??

Get an engine back, right? Your not looking for the best L/D ratio, unless you prefer to glide into the water or hills...

At 280kts, Airbus has determined that this is the best speed for a re-light for an un-assisted windmilling start. Once the APU is started, at about 25,000 ft, you can slow to green dot and commence a starter assisted re-light.

Forget about the L/D ratio !! You are trying to get an engine back and 280kts is the optimium speed for a windmilling start, until you can get down to start the APU and have it assist the starter, at which point speed can be decreased to green dot.

ahramin · Post by **ahramin** » Tue Jun 06, 2006 11:32 am

Flying at 280kts, what are you trying to do??

Get an engine back, right? Your not looking for the best L/D ratio, unless you prefer to glide into the water or hills...

At 280kts, Airbus has determined that this is the best speed for a re-light for an un-assisted windmilling start. Once the APU is started, at about 25,000 ft, you can slow to green dot and commence a starter assisted re-light.

Forget about the L/D ratio !! You are trying to get an engine back and 280kts is the optimium speed for a windmilling start, until you can get down to start the APU and have it assist the starter, at which point speed can be decreased to green dot.

Exactly guys, never mind understanding anything about glide ratios vs weight or speed. Heck why bother with principles of flight? Just do what the little screen tells you and everything will be allright.

Unless of course the little screen happens to fail, in which case understanding how it comes up with those magic numbers might not seem like such a futile endeavour

A330 the question was not why you follow the instructions but rather why the glide ratios are different. Understanding the process by which the system gets its numbers.

For those of us who think pilots should be more than simply button pushers, if i have this right the glide ratio associated with the relight speed is where you are going to hit the ground if you fly that speed all the way. The glide ratio associated with the green dot speed is where you are going to be at 3000 feet if you follow the procedure listed in the manual or the ECAM.

Thanks for the info on LAND ASAP and ECAMs in general guys.

ca787546 · Post by **ca787546** » Tue Jun 06, 2006 2:55 pm

Thank you everyone for the overwhelming response to my little question. It still remains officially unanswered, althought the explanation of considering that one will start to configure the aircraft at 3000 feet down to Vapp is as close as it has come to it, I would LOVE to know where that information can be found. I understand that you will follow the procedure, but where does it say that the relight speed of 280 kts will be maintained until down to the ground? After all, if you follow the QRH procedure, once you have altitude to use APU bleed, then you'll try a started-assisted start while decelerating to green dot. I know that some people just don't care much about the fact that the best L/D (green dot) gives you a worse glide ratio than 280kts at 70Tons, but I'd like to know. I've been flying the 320 for a couple years now, and that's a question that hasn't been convincingly answered to me yet. Well, thanks anyone to everyone that has posted so far... thrust me, in case of a dual engine failure, I'd just follow the procedure as written down, heck, I can think about the gliding ratio once I'm on the ground!
Regards,
DNB

PS: They have changed the engine dual failure procedure a few times, from 1 list, to the fuel remaining and no fuel remaining lists, and some other minor changes every now and then, so maybe it could be a typo.

ypph · Post by **ypph** » Tue Jun 06, 2006 3:34 pm

[quote]Unless of course the little screen happens to fail, in which case understanding how it comes up with those magic numbers might not seem like such a futile endeavour A330 the question was not why you follow the instructions but rather why the glide ratios are different. Understanding the process by which the system gets its numbers.

The procedure in the A330 is as follows:

RAT........................MAN ON
ENG START SEL.......IGN
THRUST LEVERS......IDLE
OPT RELIGHT SPD...300/.82
in case of a speed indication failure (volcanic ash), the pitch attititude for optimum relight speed is -2 degrees (for weights above 150 tons, add 1/2 degree for each additional 20 tons). Mach number is not indicated. Increase speed during descent towards 300 knots. Do not exceed MMo.

and the checklist goes on etc etc etc

In the sim the attitude is set using the SDBY INSTRUMENTS, in the A330-200 these are analouge and in the A330-300 its Glass.

All in all, a procedure that needs to be done in a precise manour with care taken so as to not miss things.

Premium · Post by **Premium** » Tue Jun 06, 2006 5:01 pm

Interesting question and one I cannot seem to find an answer for with my limited knowledge of aerodynamics and A320.

Max glide is accomplished at the best L/D ratio which is NOT affected by weight. The aircraft must be flown at the optimum angle of attack for any weight and this will of course cause the heavier aircraft to fly faster but still cover the same distance...just in a shorter amount of time. It doesn't make any sense how the GD glide ratio can be exceeded if it is published as the best L/D ratio.

rsandor · Post by **rsandor** » Tue Jun 06, 2006 6:20 pm

LOL. I asked 4 Delta Airlines pilots today (all 757 drivers)

None of them knew - OR CARED! LOL.

ca787546 · Post by **ca787546** » Tue Jun 06, 2006 6:37 pm

Richard, why would a 757 pilot give a rats ass about an A320 procedure? lol, and indeed, most people don't care

lol I know a few instructors in my company that don't care about it either. Some people are content with doing the procedure and leaving it at that, and that is fine because that is all that is really asked from you at the sim. I'm really intrigued by this just out of curiosity, and also because I want to learn a little about what Airbus engineers took into consideration to give those glide ratios. That's just me though!
Cheers,
DNB

PS: I remember once asking a Canadian Airlines 737 training captain what kind of flaps the 737 had, slotted or fowler (I didn't even have my private license back then) and he couldn't answer me because he didn't give a crap either, not that he needs to know, it was simply not required of him.

TOGA Descent · Post by **TOGA Descent** » Tue Jun 06, 2006 7:31 pm

ahramin wrote:
For those of us who think pilots should be more than simply button pushers, if i have this right the glide ratio associated with the relight speed is where you are going to hit the ground if you fly that speed all the way. The glide ratio associated with the green dot speed is where you are going to be at 3000 feet if you follow the procedure listed in the manual or the ECAM.

Yes, that's how it was explained to me. Remember, that Airbus doesn't "assume" that you will fly the engine relight speed all the way to the ground though.

Also, remember that in the A320 and A321 series the relight speed is 280 kts for the V2500 engines only. That speed is 300 kts for the CFM powered ships.

TOGA Descent · Post by **TOGA Descent** » Tue Jun 06, 2006 7:45 pm

A330 wrote:Flying at 280kts, what are you trying to do??

Get an engine back, right? Your not looking for the best L/D ratio, unless you prefer to glide into the water or hills...

At 280kts, Airbus has determined that this is the best speed for a re-light for an un-assisted windmilling start. Once the APU is started, at about 25,000 ft, you can slow to green dot and commence a starter assisted re-light.

Forget about the L/D ratio !! You are trying to get an engine back and 280kts is the optimium speed for a windmilling start, until you can get down to start the APU and have it assist the starter, at which point speed can be decreased to green dot.

When ca787546 posted this question, I become quite intrigued as I had never really noticed this difference in the past. Several of my colleagues were equally intrigued. Enough so, that several emails, long-distance phone calls, and personal favours (Woke up an Airbus Engineer who is a personal friend) were involved in finding the correct answer.

My point is that after flying this airplane for almost a decade, I've not found many people who completely understand it. Furthermore, I've found fewer people with the desire to fully understand it.

I have great respect for people like ca787546, who desire to better understand this airplane, opposed to simply pushing its buttons. I think it makes them far superior pilots.

rsandor · Post by **rsandor** » Tue Jun 06, 2006 8:36 pm

I have great respect for people like ca787546, who desire to better understand this airplane, opposed to simply pushing its buttons. I think it makes them far superior pilots.

Yup. I agree 100%.

except when he keeps embarassing his senior pilots by asking them questions they don't know the answers to. Then he just becomes a pain in the ass! LOL Just kiddin' buddy.

rsandor · Post by **rsandor** » Tue Jun 06, 2006 8:38 pm

Richard, why would a 757 pilot give a rats ass about an A320 procedure?

Actually I just asked thinking one of them might have airbus experience... but none did. No harm in asking.. I just like the fact that I make friends with a new crew every day.

ca787546 · Post by **ca787546** » Tue Jun 06, 2006 9:06 pm

Thanks everyone for the answers and replies. So, TOGA descent, I guess then the answer has to do with the fact that the QRH numbers are based on approximates, that the QRH procedure is considering that you will start configuring the aircraft at 3000 feet and thus slowing down from GD speed, and that if you were to use 280kts for relight (we have the V2500engines in our 320s and 319s) it doesn't take into consideration such decceleration? Ok, I guess I'm kinda happy with that. I actually considered calling our Airbus rep in the region to ask him the question, but if you asked an airbus engineer, then I will take your word for it

Thanks
Regards,
DNB

TOGA Descent · Post by **TOGA Descent** » Wed Jun 07, 2006 3:45 am

ca787546 wrote:Thanks everyone for the answers and replies. So, TOGA descent, I guess then the answer has to do with the fact that the QRH numbers are based on approximates, that the QRH procedure is considering that you will start configuring the aircraft at 3000 feet and thus slowing down from GD speed, and that if you were to use 280kts for relight (we have the V2500engines in our 320s and 319s) it doesn't take into consideration such decceleration? Ok, I guess I'm kinda happy with that. I actually considered calling our Airbus rep in the region to ask him the question, but if you asked an airbus engineer, then I will take your word for it Thanks
Regards,
DNB

Yes, that is the exaclty the explaination I received, and your summary of it is absolutely correct.

When I think about this explaination, and consider what I've learned about Airbus in the past 10 years, (As a contact Captain I've flown for about 4 airlines in the past 10 years) it makes perfect sense that they would present the QRH data in this manner.

On a separate note, my current employer has a mix of both engines, but I've always prefered the V2500 engine. It's a much better performer. I especially prefer it after a CFM engine exploded on me during a taking-off last week. Not a fun way to start your day!

TOGA Descent · Post by **TOGA Descent** » Wed Jun 07, 2006 3:49 am

rsandor wrote: Yup. I agree 100%.

except when he keeps embarassing his senior pilots by asking them questions they don't know the answers to. Then he just becomes a pain in the ass! LOL Just kiddin' buddy.

Unfortunately, my experiences have been that far too often, it's us senior pilots who embarrass ourselves, by thinking that because we’re senior, that we know everything and are never wrong.

ca787546 · Post by **ca787546** » Wed Jun 07, 2006 5:04 am

Hi TOGA descent, I don't have any experience with the CFMs but I have had to shut down a V2500 in flight due to a complete loss of oil (a faulty part was sent to us that worked fine under idle conditions but couldn't take the pressure after maintaining climb power for a sustained amount of time), and I have to admit that the engine behaved really well. It kept producing power until we got the low oil pressure ecam (you only get an advisory when oil quantity is zero, because it could simply be the sensor).
Anyhow, thanks for the info, it has helped,
cheers,
DNB

PS: If you don't mind me asking, are you currently working in Canada?

gr8gazu · Post by **gr8gazu** » Wed Jun 07, 2006 8:20 am

cpl_atc wrote:Out of curiosity, aside from fuel exhaustion, contaminated fuel, deliberate inflight shutdown (detailed in the Egypt Air QRH), and volcanic ash, what else might precipitate a dual engine failure?

I.e. if something bad enough happened to kill two jet engines, what is the hope that they can be restarted?

Compressor stalls due to high angle of attack (can also be induced by severe turbulence), very heavy rain, poor fuel management, that sort of thing.

If I only had 2 and none were turning, I would try a relight for any cause of the failure...

A330 · Post by **A330** » Wed Jun 07, 2006 8:32 am

The 280 kts, is not a glide ratio or L/D ratio speed. It is a recommended speed to move the engine fans to a speed that will give the best chance for re-light.

If there is no chance for re-light and the engines seized for example or you ran out of fuel, then green dot, best L/D, would be the best option for maximizing time/distance. After Transat, there is now a paper procedure for all engine flameout with fuel and without fuel. If you ran out of fuel, ie no chance of starting engines, then it says to immediately slow to green dot for maximum glide ratio. So at 280 kts you are notgetting a better glide ratio; you're just trying to get an engine back. And remember the QRH can be filled with small mistakes...

Ahramin....

As moderator, shouldn't you be setting an example of a balanced response? That was quite foul.... having never flown these airplanes you should zip it.

HavaJava · Post by **HavaJava** » Wed Jun 07, 2006 8:47 am

A330,

I don't think you get the point of this discussion. None of your posts have done anything to contribute to the original question. You may very well be right that this is a typo but if it is then why not bring it up so it can be changed.

No one is arguing that best glide speed is not GD.

TOGA Descent · Post by **TOGA Descent** » Wed Jun 07, 2006 9:04 am

ca787546 wrote: PS: If you don't mind me asking, are you currently working in Canada?

Nope. Asia. I assume that you are in Canada.

A330 · Post by **A330** » Wed Jun 07, 2006 9:07 am

Ok, fair enough...

Let me try again,

If you point the nose down and try to obtain 280 kts, you are losing altitude at a faster rate than slowing to green dot and maximizing distance. I think the posted glide distances are rough at best. Green dot will give you the best glide distance if you lose both engines with no chance of a re-light. Flying at 280kts after a dual flameout, you will fall out of the sky and hit the ground a lot sooner than slowing to green dot. The info in the QRH is misleading.

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

Does that sound reasonable?

TOGA Descent · Post by **TOGA Descent** » Wed Jun 07, 2006 9:08 am

A330 wrote: And remember the QRH can be filled with small mistakes...

Ahramin....

As moderator, shouldn't you be setting an example of a balanced response? That was quite foul.... having never flown these airplanes you should zip it.

Airbus QRH is full of "Assumptions". Airbus would be most offended - typical french - if you told them that they made mistakes (Doh!). Second note, you are absolutely correct. If you haven't flown, or at least qualified on, the aircraft, zip it!

HavaJava · Post by **HavaJava** » Wed Jun 07, 2006 9:11 am

A330,

Yes, that sounds reasonable and I don't think anyone has argued against what you said.

I just don't think that you have contributed anything of meaning to ca787546 question.

TOGA Descent · Post by **TOGA Descent** » Wed Jun 07, 2006 9:14 am

cpl_atc wrote:Out of curiosity, aside from fuel exhaustion, contaminated fuel, deliberate inflight shutdown (detailed in the Egypt Air QRH), and volcanic ash, what else might precipitate a dual engine failure?

Don't know. Sun spots? George Bush? The list is hardly short of exhaustive.

Sorry, been out drinking in SE Asia. You don't know that that can do to you senses. Not to me mention your spelling and vocabulary.

A330 · Post by **A330** » Wed Jun 07, 2006 10:24 am

The increase in glide distance for the initial speed of 280, would be greater due to the increased distance covered initially. The problem is that maintaining that speed brings you closer to the ground in less time, and therefore distance versus if you slowed to green dot. That's the point; the 2.7nm/1000' ( if that's correct ) is a temporary figure...the 280kt speed will reduce your glide time/distance if you do not get an engine back.

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.

How's that for meaning?

Premium · Post by **Premium** » Wed Jun 07, 2006 10:30 am

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.