DL1170 ATL-MSY MD88 in-flight "incident" 8/26, Expert/Insider input requested

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Hello to everyone, I am a long time lurker and this is my first post to airliners.net. I had something unusual happen on DL1170 ATL-MSY on 26 August that I would appreciate any input on what might have happened from the experts and/or insiders on airliners.net (I am something of a nervous flyer and was very anxious through the rest of the flight). I will do my best to relate what happened.

We left ATL late due to weather backups in Atlanta and delay on the incoming aircraft (MD88). Took off into perfectly smooth air and were at or coming up to cruising altitude (at least we seemed to be) approximately 15-16 minutes into the flight when, in otherwise smooth air, a fairly loud and tactile vibration occured in what seemed like the fuselage (as opposed to a wing or motor). I was in 2C and it felt to originate in the front underside of the aircraft although this could certainly have just been my perception of the location. The vibration lasted about 4-5 seconds, stopped, and then occured again, exactly the same, about 2-3 minutes later. It seemed at that time that the pilots disengaged the autopilot and backed off slightly on the throttle. The cabin crew was very professional, but it was clear this was unusual to them as well and they moved into emergency preparedness mode. The pilot came on a few minutes later and said that they were unsure of what had caused the vibration, but the aircraft was currently flying normally and responding to all of their input. He came back on several minutes later to say that they were not showing anything wrong with the aircraft, again reiterated that the plane was flying and responding normally, alluded to an idea of what had happened but did not say what he thought it was, and told us that we would be met on the runway by emergency vehicles to be inspected. The remainder of the flight was smooth and without incident (save my sweaty palms and racing heart), we landed, were inspected, and proceded to the gate without any other problems. I noticed that the outgoing flight for the aircraft the next morning was cancelled, but wasn't able to find out anything else about what happened.

Does anyone have any ideas or any actual knowledge of what might have happened? It was definitely not like anything I have ever experienced in a plane before (turbulence, rough landings, the like). Your input is greatly appreciated!! For those who read both, I posted this to the Delta forum of flyertalk.net and got a little feedback and some discussion on the MD-88, but not really what I was hoping for.

You can hear the communications with MSY Tower here:

http://archive-server.liveatc.net/kmsy/KMSY-Aug-27-2007-0230Z.mp3

and the Pilots suspected possible left engine thrust reverser deployment in flight.

Quoting 71Zulu (Reply 1): You can hear the communications with MSY Tower here: http://archive-server.liveatc.net/kmsy/KMSY-Aug-27-2007-0230Z.mp3 and the Pilots suspected possible left engine thrust reverser deployment in flight.

FYI to all the relevant section starts 7:12 in to the linked clip.

Quoting 71Zulu (Reply 1): and the Pilots suspected possible left engine thrust reverser deployment in flight

I believe an in flight thrust reverser deployment brought down a Lauda 763 in the 90's.

Quoting 71Zulu (Reply 1): and the Pilots suspected possible left engine thrust reverser deployment in flight.

At about 26:42 into the tape, the FD mentions that both engines look identical.

I tend to doubt it was a thrust reverser. When one deploys in-flight, it's usually not a "suspect it" kind of situation--it's pretty clear with all the noise, drag, and yaw. That assumes a full deployment, of course, and I guess the possibility is there that it could have unlocked and become only partially deployed. Based on the OP's comment that "it felt to originate in the front underside of the aircraft", I'd guess it was maybe a nose gear door or servicing panel (lav door?) was somehow involved.

Years (and years) ago, I had bummed a ride LFT-HOU on a Turbo Commander, and was listening to the SWA freq. on the way back. I heard a HOU-MSY flight that was landing at BPT due to a vibration somewhere in the lower nose section on the F/O's side. After they blocked in at BPT, it became readily apparent what the problem was. After the ramper had walked the aircraft out on pushback at HOU, he'd taken his headset off and hung it on the open access door, and then went to the nosegear to disconnect the towbar. After he did, he then waved the aircraft out. At BPT, they found the headset cord still plugged in, and about a 10-foot length of cord hanging back that had been whapping the side of the aircraft. The headset itself was subsequently found adjacent to the right side of the runway at HOU.

I'd be kind of curious as to what Delta's ended up being.

We used to find loose/open servicing panels all the time..nothing new. Now could the small ground-power door do that? Highly unlikely.

DeltaGuy

Quoting DeltaGuy (Reply 5): We used to find loose/open servicing panels all the time..nothing new. Now could the small ground-power door do that? Highly unlikely.

Maybe, maybe not. On the one years ago, the crew had difficulty with getting the airspeed up (the comm door was partially bent backwards), and they too had vibrations. It doesn't take much at higher speeds to produce them when something isn't aerodynamically where it should be....

Too many unknown details with the DL case. Did they have the vibration only on the climbout, or also at cruise or descent?

Did you happen to get the tail number of the aircraft involved?

An agent at my station once left the Comm door open on the nose of a CRJ... the FO described it as the sound of a 4 year old playing a clarinet all the way to CVG...

Quoting MSYtristar (Reply 3): I believe an in flight thrust reverser deployment brought down a Lauda 763 in the 90's.

This is correct, which begs the question:

If deployment of the thrust reverser is disastrous as in that case, why would the pilots suspect it when obviously they hadn't lost control and crashed? Just the thrust differential being closer to centerline on an M88 than a 763?

On that note, why would thrust reverser deployment be disastrous? It seems to me that if you shut down the engine it was deployed on, you would just have a regular engine-out situation. And in the Lauda case, they had advance warning of a problem with the thrust reverser so they would be able to shut down the correct engine immediately. What am I missing?

Quoting DL787932ER (Reply 9): On that note, why would thrust reverser deployment be disastrous? It seems to me that if you shut down the engine it was deployed on, you would just have a regular engine-out situation

I think it is a question of timing. My friend told me that per the Boeing flight manual, the pilots only have about a two second window to react when they see that thrust reverser deployed light illuminated. They need to go full aileron and shut the engine in question down almost immediately or the airplane will roll hard over and it would be impossible to recover.

Don't know if this helps... but this is why the flight CXLD the next morning

8/27/2007 6:30:06 AM A R FLT CXLD - MECHANICAL ON SH9018 - ENGINE

A TR deployment in flight will not bring down a MD80 like in the Lauda air accident. MD actually proved it during test flights. I think it has to due with engines being closer to the centerline. I'll try to look into the incident if I get a chance tonight.

The Md-80 series have the "clamshell" type reverser system. These are obviously different than the engine types on 75's, 76's, etc. The GE,RR, and trent models on the boeings and airbuses , actually reverse the thrust don't they? The clamshells just move over the exaust and use that to slow the aircraft down, right? Either way, that sudden loss of thrust would be fairly violent.

I listened to the whole set of ATC. But I'm concerened that we didn't hear what acutally happened enroute. It sounds like an issue that affected the aircraft at cruise but wouldn't be the engines reversers. Professional pilots handled the problem but we still have no clue what the real problem was. The fire services in MSY saw no differences between right and left engines so thust reversers couldn't have been the problem? What did DL maintenance find that canceled the next flight for that aircraft?

I fly DL on a regular basis and would like to know. What really happened?

GJSINT172

Absolutely brilliant!! Thanks to everyone for the replies so far, the ATC clip is incredible. Hopefully we will find out what maintenance actually found. Interesting that the pilots thought the vibration originated in the engines when I thought it came from the front (I guess sound and vibration traveling through aluminum traveling 450kts can be deceiving). It is hard to fathom that the problem was a thrust reverser though unless it was just partially deployed as there was no sudden movement of the aircraft or abrupt deceleration, but what do I know? Thanks again, looking forward to any further information.

I checked on the plane last night. One of the T/R's was on the MEL list at the time, so it was locked out. Because of this the crew most likely jumped all over that as the reason for the abnormal flight. They verified the TR was locked and then did a full boroscope inspection on both engines due to suspected engine surging. Both engines were fine and the aircraft was put back in service. The T/R was fixed a couple of days later and it has been flying around with no problems.

Hate to ask a dumb question, but what is a MEL list? I guess the source of the vibration will remain unknown. Thanks so much for all the responses.

Quoting Wplong1 (Reply 17): what is a MEL list?

Minimum Equipment List...aircraft can operate with broken equipment due to redundancies or the broken part isn't needed (ie: thrust reverser...you still have wheel brakes). If the broken part qualifies as redundant or not needed, and it doesn't affect the safety of flight, it is put on the MEL. This way, the aircraft never leaves service, which could cause disruptions if a spare is not available or the aircraft is at a non-maintenance station.

Just to add to what LawnDart said about the MEL list; each item on the list has a specific length that the system can be inop and in some cases certain conditions must be met to keep flying. Some items can only be inop for a day or two. Most are in the ten day window, while some can be for months. Some conditions that have to be met are repetitive inspections until it is fixed or operating limitations, like runway length or flight into known ice. The MEL list is what really lets an airline keep flying. The FAA keeps a close watch on the daily count for each airline and watches for repeat appearances. I know our managers really put an emphisis on clearing these items every night if possible. We are expected to take a look at every item 'on the hook'. If we can't fix it, have something to add to the log on troubleshooting the problem.

Quoting DALMD88 (Reply 19): and in some cases certain conditions must be met to keep flying.

..and I can attest to the fact that dispatchers are keen to keep aircraft with restrictive MEL items out of prohibted conditions like low viz, icing, etc., or altitude and/or speed restrictions. (Hint to crews: this is just one factor that may be behind the reason you got one of those ever-popular "bag-drags" (aircraft swaps) when you didn't expect one...)  

Would be interesting to know the reg of this A/C..if anyone finds out, please post it here.

Very interesting. Good audio clip. Can imagine that is a bit scary. Glad it all went OK.

If they were thinking TR problem am surprised they did not shut down suspected engine (or maybe did not know if it was L or R) and 16 minutes into flight would it not have been better to return to ATL for safety and logistically? Not judging crew, obvioulsy they handled it very well -- just a question.

Is there tape of when they declared the emergency initially. Assuming this was "PAN PAN"? MSY controller already knew when this MP3 file started.

How do you get audio archives like -- how do you know where/when to look for them (time lsot, etc.)?

Always impressive to hear how cool and professional everyone is in the dialogue. Even though many pilots would say this is another day at the office, having a perceived problem like this would be a tough day in the front office.

Quoting Mika (Reply 21): Would be interesting to know the reg of this A/C..if anyone finds out, please post it here.

Ship Number 9018 is N918DE

All 9xx series (901 to 999) are N9xxDL, except 927 is N927DA and 999 is N999DN

All 90xx series (9000 to 9020) are N9xxDE

This is the site where you can hear Live ATC feeds from selected cities and thanks to the enthusiasts who donate their time, equipment and effort to get these feeds on-line and I am lucky to have a feed at my home airport.

http://www.liveatc.net/

These feeds are also archived for 30 days by Greenwich Mean Time or Zulu Time, which for MSY during daylight savings time is local time +5 hours, so for the approximately 9:45pm arrival of this flight, that would be 0245 Zulu Time the following day.

Convert local time to GMT here:

http://wwp.greenwichmeantime.com/



There is no ATL feed that I am aware of on this site but there may be on another site.

I would assume that the ATL or enroute controller called MSY by phone and informed them of the situation and the Captain's intention to continue to MSY.

Yes, this was professionally handled and it was nice to be able to hear the whole thing as it happened.

Thanks for the links/info 71Zulu!

I highly doubt this was a thrust reverser issue. I can't imagine the pilots continuing the flight if that was the case. The Lauda Air 767 showed us the tragic consequences of a thrust reverser deployment in flight. The TAM F100 proved it is just as catastrophic on a rear engined aircraft with thrust differential closer to centerline. I don't know the specifics about the MD-80 flight tests from back in the day, but for the two crashes mentioned, recovery was virtually impossible.

Quoting 71Zulu (Reply 24): There is no ATL feed that I am aware of on this site but there may be on another site.

There is: http://atcmonitor.com/

It has approach and ATL tower.

Must have been a dull night for the MSY controller with combined frequencies lol. He was working the plane as MSY tower more than 15 miles out.

XJR

Quoting TrijetsRMissed (Reply 26): I highly doubt this was a thrust reverser issue. I can't imagine the pilots continuing the flight if that was the case.

I can't imagine the pilots not having controllability issues if the T/R deployed.....look at it from an aerodynamics point of view. An MD-80, going what 450kts...now remember how an MD-80's T/R's are designed, as clamshells. Were there to be a deployment, at cruise speed, it seems to me that the air stream would force them into a full deployment. The aircraft would then immediately either roll over and go into a dive, or seriously yaw, then roll over.

Nope, no way was it a T/R issue.

Quoting XJRamper (Reply 28): Must have been a dull night for the MSY controller with combined frequencies lol. He was working the plane as MSY tower more than 15 miles out.

DL 1170's scheduled arrival is 8:15pm local.....by that time of day traffic has slowed down somewhat, at least the departure side has, and the tower can combine up some of the frequenices. Not so uncommon as you might think, and MSY's definitely not unique in that way.

Tom at MSY

Quoting Tom in NO (Reply 29): can't imagine the pilots not having controllability issues if the T/R deployed.....look at it from an aerodynamics point of view. An MD-80, going what 450kts...now remember how an MD-80's T/R's are designed, as clamshells. Were there to be a deployment, at cruise speed, it seems to me that the air stream would force them into a full deployment. The aircraft would then immediately either roll over and go into a dive, or seriously yaw, then roll over.

Well it just isn't the case. I've searched the internet for a copy of the test but I couldn't find it. I saw it while I was in MD88 school. They deployed a single T/R while in flight and had no controllablity issues. I'm sure they did have some yaw but they were able to counteract it just fine.

Quoting DALMD88 (Reply 30): I saw it while I was in MD88 school. They deployed a single T/R while in flight and had no controllablity issues. I'm sure they did have some yaw but they were able to counteract it just fine.

That is pretty damn impressive, I'd love to see that test. The MD-80 has always had a great safety record.

Quoting DALMD88 (Reply 30): Well it just isn't the case. I've searched the internet for a copy of the test but I couldn't find it. I saw it while I was in MD88 school. They deployed a single T/R while in flight and had no controllablity issues. I'm sure they did have some yaw but they were able to counteract it just fine.

I'm not being contradictory here, but have well over 10,000 hours in the DC-9 and the MD-80 series, and this goes against everything I have ever been taught, and certainly goes against the simulation I have seen, which is both impressive and scary. I would very much to see this test data. I'm not saying that the aircraft wasn't able to be controlled, but I am confident that it took a very high degree of proficiency and airmanship. Mercifully the T/Rs on the aircraft are extremely reliable, and I do not have any personal experience with one opening in flight, and I'd just as soon keep it that way.

Quoting TrijetsRMissed (Reply 31): That is pretty damn impressive, I'd love to see that test. The MD-80 has always had a great safety record.

Yes it would be an impressive test. I wouldn't want anything to do with it. You are right that the MD-80 has a great safety record. It's built like a tank: it works good and lasts a long time.

I've seen the same McDonnell Douglas marketing footage of an MD80 in flight with a T/R deployed. (Yep, while attending the MD88 FAM @ DAL), in the video, MD plays it off as a minor inconvenience.