Not the best time for an unstable approach

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pelmet
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Not the best time for an unstable approach

Post by pelmet »

N813NW, an Airbus A330-323 aircraft operated by Delta Air Lines, was conducting flight DAL70 from Atlanta, GA (KATL) to Amsterdam, Netherlands (EHAM). About 557 nm northeast of Goose Bay, NL (CYYR), the flight crew noted number 2 engine vibrations and initially elected to divert to Detroit, MI (KDTW). As the flight crew continued to monitor the engine condition, a decision was made to divert to CYYR instead. Due to an unstable approach on CYYR runway 26 , the crew carried out a missed approach.

When power was added for the go around, loud bangs were heard and the flight crew noted that the number 2 engine (Pratt & Whitney PW4168A) had failed. The
flight crew carried out the single-engine go-around procedure, declared an emergency, and completed the QRH procedures to secure the failed engine. A single-engine landing on CYYR RWY 08 was carried out uneventfully.

After the aircraft shutdown, damage was noted to the number 2 engine pressure relief doors. When viewed from aft through the engine exhaust duct, turbine blade damage was evident. Foreign object to the lower flap skin and flap track fairing aft of the number 2 engine was also observed.
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fish4life
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Re: Not the best time for an unstable approach

Post by fish4life »

If anything I think it shows a high level of professionalism that the crew was diverting for an engine issue, realized they were unstable and didn’t try to “force it in there”.
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pelmet
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Re: Not the best time for an unstable approach

Post by pelmet »

Still not the best time for an unstable approach.
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complexintentions
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Re: Not the best time for an unstable approach

Post by complexintentions »

So when IS the best time for an unstable approach, exactly?
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Re: Not the best time for an unstable approach

Post by confusedalot »

I am trying to figure out where the problem is.
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Re: Not the best time for an unstable approach

Post by ninjacrumb »

Frustrating isn't it Pelmet? Three guys don't get what you're saying.

I agree though, when you have a dud engine better make sure your approach is planned 100%
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Re: Not the best time for an unstable approach

Post by complexintentions »

Oh I got what he's saying. He chose to emphasize the fact that the first approach was unstable, instead of commending the discipline demonstrated by performing a go-around with a sick engine.

I'm sure the approach "was planned 100%". But in a non-normal situation there are always things that happen that make the best of plans not quite work out. That's when (circumstances and time permitting) a professional crew tries again. I highly doubt the first approach was unstable because the crew was inadequately prepared. The fact the first approach was to RWY 26 and they landed on RWY 08 suggests that perhaps the wind changed, hmm? There are any number of reasons an approach can become unstable.

A single-engine g/a is a procedure that is trained for. An unstable approach continued to landing carries far higher risk. They made exactly the right decision. Trying to highlight the fact that the first approach was unstable without even knowing why is just petty. Which is a bit of a theme with the thread originator.

Nothing to see here, a job well done.
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Re: Not the best time for an unstable approach

Post by linecrew »

Not knowing anything about anything...is it common practice to apply go-around power to an engine that is vibrating and was the actual reason for the diversion? Sounds like this action kinda blew the engine apart. Could they have carried out a go around with that engine left at idle power? Again...I don't know my a$$ from my elbow regarding this stuff, which is why I am asking.
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pelmet
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Re: Not the best time for an unstable approach

Post by pelmet »

linecrew wrote: Thu Nov 23, 2017 8:48 am Not knowing anything about anything...is it common practice to apply go-around power to an engine that is vibrating and was the actual reason for the diversion? Sounds like this action kinda blew the engine apart. Could they have carried out a go around with that engine left at idle power? Again...I don't know my a$$ from my elbow regarding this stuff, which is why I am asking.
That might be a question that ComplexIntentions can answer for you. After all, he seems pretty sure that it "was planned 100%". But...it looks like our linecrew is more on the ball than our flightcrew.

Some might remember the criticism of a King Air crew in YVR that didn't shut down a faulty engine and the consequences of the crash. This situation is quite different in that there is not the worry of the drag of a windmilling propeller and there may a desire not to do a shutdown to prevent an effect on the ETOPS record. The QRH doesn't even say to shut the engine down.

OK...so you decided to leave it running and divert. But there is a reason for that vibration and perhaps one should consider treating it as a failed engine and disconnect the autothrottle at some point(or as appropriate for an Airbus in such a situation). And if you have to go around.....leave the faulty engine at idle or a lower power setting, perhaps disconnecting the autothrottle at the latest, once a go-around decision has been made. Otherwise, your command for go-around thrust might damage the engine and airframe(as happened here) or even worse....damage people.
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Last edited by pelmet on Thu Nov 23, 2017 12:47 pm, edited 3 times in total.
FICU
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Re: Not the best time for an unstable approach

Post by FICU »

Better to use all available thrust during a go-around and deal with a bad engine later especially in mountainous terrain. As Complex mentioned they probably tried a tailwind approach and couldn’t get it stabilized so did what they should have and went around.

If a checklist didn’t lead to shutting the engine down you don’t make up your own procedure in a 2 engine go-around by leaving one at idle.
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Re: Not the best time for an unstable approach

Post by pelmet »

FICU wrote: Thu Nov 23, 2017 11:19 am Better to use all available thrust during a go-around and deal with a bad engine later especially in mountainous terrain. As Complex mentioned they probably tried a tailwind approach and couldn’t get it stabilized so did what they should have and went around.

If a checklist didn’t lead to shutting the engine down you don’t make up your own procedure in a 2 engine go-around by leaving one at idle.
There is no particular guidance that I can find in Boeing or Airbus manuals for this situation of a go-around in such a situation, which is perhaps intentional. Everything seems to assume that a landing is accomplished.

Keep in mind that in the previous post I said idle OR A LOWER power. As the A330 checklist for engine high vibration does say "If flight conditions permit, reduce thrust to maintain vibration level below the advisory threshold", it does give allowance for this. Whether this includes at least certain go-around situation is not discussed.

While I do understand your point, this case appears to show the potential adverse consequences of adding high power to an faulty engine in this situation....ie secondary damage to the wing and flaps in this case which fortunately did not lead the further detrimental consequences in flight.

Thanks for the reply.
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Re: Not the best time for an unstable approach

Post by FICU »

If the checklist requires you to run at a reduced thrust setting then it should lead you to the procedures for a single engine approach so in the event of a go-around you would be properly configured with less flaps, 15 as opposed to 30 or 40 for a Boeing. Don’t know anything about Bus procedures.

Follow the SOP.
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Re: Not the best time for an unstable approach

Post by pelmet »

Content moved to a later post due to added info. No way to erase this post.
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Last edited by pelmet on Fri Nov 24, 2017 10:29 am, edited 4 times in total.
goingnowherefast
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Re: Not the best time for an unstable approach

Post by goingnowherefast »

I'd imagine the crew wasn't blindly following the checklist either. They likely had their company dispatch and maintenance well aware of the situation and making well educated suggestions. Who know what sort of engine data was being sent back to the maintenance department allowing engineers to make decisions that were more informed than a procedure written prior to the event.

Don't forget, they did have quite a bit of time on their hands as the issue first became apparent 557nm from their final point of landing. They had also initially planned to divert to Detroit, several hours to diagnose the problem more accurately than "it's vibrating and the checklist says ____". Why did they change their diversion plan? I bet it had something to do with their maintenance and dispatchers.
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pelmet
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Re: Not the best time for an unstable approach

Post by pelmet »

FICU wrote: Thu Nov 23, 2017 3:31 pm If the checklist requires you to run at a reduced thrust setting then it should lead you to the procedures for a single engine approach so in the event of a go-around you would be properly configured with less flaps, 15 as opposed to 30 or 40 for a Boeing. Don’t know anything about Bus procedures.
Not true actually. Not all Boeing's have a flap 15 landing for situations with reduced thrust. That may apply to certain aircraft like the 737. But some Boeing types allow full flap landings in a reduced thrust situation including engine-out if performance allows(ie. they don't lead to procedures requiring less flaps). They simply say that if performance allows, a full flap landing is allowed which is no different than for normal landings where flap selection can be restricted by go-around performance. Procedures obviously vary by type.

The old 727 was restricted to flap 15 landings for operators going into La Paz. Not sure what they did in an engine out situation.

As for "follow SOP", there is no SOP for this situation written down in terms of what to do in the event of a go-around with a bad engine that is still operating. Take a look at the typical surge, limit, stall checklist. The thrust is reduced and if the engine parameters can remain within limits, then the engine is allowed to be kept running. This could easily be at idle only where it can be kept within limits. Does the SOP somewhere say that it is OK to go back to full go-around thrust somewhere due to a go-around? I think not. You are expected to keep the engine within operating limits which may very well be at idle unless under the authority of the PIC, it is determined that for the purposes of an emergency, this potential engine thrust is required.

While the details of this incident are unknown to us, I don't think that it was a coincidence that this engine blew apart during a go-around. It is more likely that during the go-around a lot of power was added. This can make things worse, whether it is the situation that happened here or multiple distracting compressor stalls. Ask yourself something. You discover that an engine has really bad compressor stalls over and over and can only be operated normally at the near idle position. During the approach It is decided to go-around. Are you really going to add full power to the engine that you know will be making big compressor stalls as soon as significant power is added? The SOP is actually following the checklist that says on one Boeing type..."Run the engine normally or at a reduced thrust that is surge and stall free". If that is at idle then that is at idle. It doesn't mean that one should ignore this statement for a go-around. If you ever hear compressor stalls on a big engine, you will really understand why. While I don't know the exact details of this flight, but if the approach in my scenario "was planned 100%", it would include not adding thrust on the faulty engine unless absolutely required.

As for the cause of the unstable approach, I prefer not to make any assumptions based on no information such a windshift as has been done in a couple of posts on this thread. The weather for that day shows winds steady out of the south appearing to make either 08 or 26 suitable.
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Last edited by pelmet on Fri Nov 24, 2017 10:55 am, edited 1 time in total.
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Re: Not the best time for an unstable approach

Post by FICU »

Would you plan a flaps 30 or 40 landing knowing you are leaving one engine at idle thrust(because it’s sick or to prevent further damage) in the event of a go-around? There is a reason engine out approaches are done at reduced flap settings and doing an approach with 1 engine at idle is essentially a single engine approach.

So a couple of options... plan a normal landing and use all available thrust in the event of a go-around or protect the engine and treat it is a single engine approach in the event of a go-around. Looks like the crew in this incident used option 1.
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Last edited by FICU on Fri Nov 24, 2017 11:12 am, edited 1 time in total.
pelmet
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Re: Not the best time for an unstable approach

Post by pelmet »

FICU wrote: Fri Nov 24, 2017 10:53 am For high engine vibs or surge/stall, for example, if the checklist tells you to operate at reduced thrust and plan a normal flap landing then it is expected to use all available thrust in a go-around.

Would you plan a flaps 30 or 40 landing knowing you are leaving one engine at idle thrust(because it’s sick or to prevent further damage) in the event of a go-around?
All available thrust on a go-around when one has a problem is all available within the limits of what the engine is capable of doing. I certainly have no intention of adding thrust to an engine that is going to start compressor stalling when I know will have to immediately bring it back to where it was before. Aside from scaring the hell out of the passengers again, it just makes things unnecessarily complex for the pilots.

As for the flap settings you mention...there are differences between our aircraft types so I won't comment on the specific settings you mention but just say that I would normally choose the lower setting of the two options given on the type I fly. However, that is personal preference based on full flap being allowed if performance allows.



I see you since changed your post and are now saying....
FICU wrote: Fri Nov 24, 2017 10:53 amSo a couple of options... plan a normal landing and use all available thrust in the event of a go-around or protect the engine and treat it is a single engine approach in the event of a go-around. Looks like the crew in this incident used option 1.
Looks like option 1 blew up the engine. I suggest considering option 2.

Complex has disappeared again(like our last debate) so I guess he has changed his mind again and agrees with me again.
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Last edited by pelmet on Thu Nov 30, 2017 5:22 pm, edited 4 times in total.
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Re: Not the best time for an unstable approach

Post by skybluetrek »

This debate of the incident reminded me of an accident, the TAM3054, when after a challenging approach the Capt. got confused between two different procedures and ended up mistaken engines when applying throttle settings upon landing.
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