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Inflight Reverse Thrust On DC 8  
User currently offline6YJCX From Jamaica, joined Dec 2007, 23 posts, RR: 0
Posted (6 years 4 months 2 weeks 3 days 16 hours ago) and read 8599 times:

In the early 1980's I was on an Arrow Air DC-8 from NAS to MIA when the captain announced that we were a bit high on downwind to MIA 9R and that the vibration that was soon to start was the thrust reversers on the two inboard engines. I recall saying to my wife that this guy cant be serious, but he was. We were probably at fl180 or thereabouts coming up on the coast and within the next half minute or so were low and slow. How was this possible? It was not long after that when a Lauda Air 767 went down in Asia from tr deployment of one engine, according to accident reports and I often wondered if there were no lockouts to prevent this.

That old DC-8 shook and rattled when the reversers were set and I recall how unfortunate we were to be on this airplane, which was pressed into service to transport passengers stranded by an UP 737 that was taken out on mx issues. The DC-8 crew seemed to have been hauled off the beach to take this instant charter judging from the speed of the flight was obvious in a hurry to return to tanning.

21 replies: All unread, jump to last
 
User currently offlineRFields5421 From United States of America, joined Jul 2007, 7345 posts, RR: 32
Reply 1, posted (6 years 4 months 2 weeks 3 days 16 hours ago) and read 8563 times:

The basic answer - They were designed for that usage.

But you mentioned the key factor in the Lauda crash - asymmetrical TR deployment.

Pretty much anything you do in an airplane is BAD if it happens on one wing only and there is no balancing action on the other wing.


User currently offlineKiwiandrew From New Zealand, joined Jun 2005, 8492 posts, RR: 14
Reply 2, posted (6 years 4 months 2 weeks 3 days 16 hours ago) and read 8555 times:
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I believe that certain models of the DC-8 had the ability to 'pre-arm' reverse thrust so that as soon as the wheels touched it would activate automatically , however , IIRC , at least two crashes ( AC ? and Loftleidir? ) were caused by the reverse thrust being inadvertently activated rather than just armed while still airborne - I am sure that somebody on Anet will have far more info on this subject than I do .

With the NG 767 I believe it was a very different situation ( I had just arrived in London on a CP 763 at the time the news broke and initially it was thought that there might have been a terrorist bomb before the actual cause came to light - as we had been delayed in departure from YYZ the night because they had to offload bags from a pax who failed to board I remember feeling very grateful that the airline had played safe and taken that action ) IIRC it was widely attribute to an electrical failure leading the reverser to activate and I believe subsequently a locking mechanism was developed to prevent a recurrence



Moderation in all things ... including moderation ;-)
User currently offline727forever From United States of America, joined Jan 2006, 793 posts, RR: 5
Reply 3, posted (6 years 4 months 2 weeks 3 days 16 hours ago) and read 8531 times:

The DC-8 does not have flight spoilers to assist with getting down quickly. Instead Douglas designed it with the ability to select idle reverse on engines 2 and 3 which is quite effective. I've not flown the 8 as a crew member but have seen it done quite a few times riding in the jumpseat. Surely there are a few 8 drivers on anet that would care to pipe in with better details.

727forever



727forever
User currently offlineRFields5421 From United States of America, joined Jul 2007, 7345 posts, RR: 32
Reply 4, posted (6 years 4 months 2 weeks 3 days 16 hours ago) and read 8517 times:

The C-17 has something similar to the DC-8.

I'll have to wait for an answer from a friend who flies them as PIC - but they allow the plane to make incredibly steep descents and not gain a huge amount of speed.

I've also read about a Gulfstream II NASA modified to Space Shuttle training where the TR deploy to simulate the high descent rate of the Shuttle.


User currently offlineVisityyj From Canada, joined Jun 2000, 519 posts, RR: 0
Reply 5, posted (6 years 4 months 2 weeks 3 days 16 hours ago) and read 8462 times:

Air Canada DC-8 crash was caused by premature deployment of the spoilers while still flying. Nothing to do with reverse. http://aviation-safety.net/database/record.php?id=19700705-0

User currently offlineAviateur From United States of America, joined Apr 2004, 1350 posts, RR: 12
Reply 6, posted (6 years 4 months 2 weeks 3 days 16 hours ago) and read 8452 times:

I flew a DC-8F. Our airline prohibited the use of in-flight reverse, even though Douglas had certified the plane for it.

PS



Patrick Smith is an airline pilot, air travel columnist and author
User currently offlineKiwiandrew From New Zealand, joined Jun 2005, 8492 posts, RR: 14
Reply 7, posted (6 years 4 months 2 weeks 3 days 16 hours ago) and read 8452 times:
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Quoting Visityyj (Reply 5):
Air Canada DC-8 crash was caused by premature deployment of the spoilers while still flying. Nothing to do with reverse. http://aviation-safety.net/database/...705-0

ooops , my mistake - thanks for putting me right Big grin



Moderation in all things ... including moderation ;-)
User currently offlineArrow From Canada, joined Jun 2002, 2675 posts, RR: 2
Reply 8, posted (6 years 4 months 2 weeks 3 days 16 hours ago) and read 8404 times:
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Quoting Kiwiandrew (Reply 2):
IIRC , at least two crashes ( AC ? and Loftleidir? ) were caused by the reverse thrust being inadvertently activated rather than just armed while still airborne

That was a spoiler deployment, not a thrust reverser. First officer moved to arm spoilers for automatic deployment on touchdown, but pulled the lever all the way and inadvertently deployed them while the aircraft was still a hundred feet above the runway. Douglas changed the design of the arming mechanism so you couldn't do that.

I was on an AC DC-8 from Vancouver to Calgary when they deployed the inboard thrust reversers to get down in a hurry. It did shake the plane a little, and the pilot announced the move before he did it.



Never let the facts get in the way of a good story.
User currently offlineTimz From United States of America, joined Sep 1999, 6708 posts, RR: 7
Reply 9, posted (6 years 4 months 2 weeks 3 days 16 hours ago) and read 8389 times:

Wasn't there a DC-8 (Alitalia?) crash caused by inflight reverse with some flap out-- which isn't allowed?

User currently offlineDtwclipper From , joined Dec 1969, posts, RR:
Reply 10, posted (6 years 4 months 2 weeks 3 days 16 hours ago) and read 8373 times:



Quoting 6YJCX (Thread starter):
That old DC-8 shook and rattled when the reversers were set

I was on an Icelandic '8 back in the 80's (LUX-KEF-JFK) and had the same experience. It was a pretty fun ride!


and oh, here's another thread on the topic:

DC-8 And Reverse Thrust Use In Flight (by Ttailsteve Jul 3 2006 in Civil Aviation)


User currently offlineFWI747 From France, joined Jul 2007, 71 posts, RR: 0
Reply 11, posted (6 years 4 months 2 weeks 3 days 15 hours ago) and read 8265 times:

Adding my two cents to the link posted by Dtwclipper : back in 1994, I was on a Minerve flight CFM 56 powered DC-8 which performed an in-flight use of the thrust reversers, very impressive and not that shaky !!

Probably one of its last rev flight, I wish I could fly on a plane with such a feature again !

David


User currently offlineAirfoilsguy From , joined Dec 1969, posts, RR:
Reply 12, posted (6 years 4 months 2 weeks 3 days 15 hours ago) and read 8235 times:

The Concord could use thrust reverse in flight as well, though I might be wrong.

User currently offlineBlackbird From , joined Dec 1969, posts, RR:
Reply 13, posted (6 years 4 months 2 weeks 2 days 18 hours ago) and read 7936 times:

From what I remember about the DC-8, the plane was originally supposed to use a split-brake type system a'la the F-86 Sabre and thrust-reversers. Both of which were to be used to slow the plane down. The speed-brake turned out to be almost useless and the reversers turned out more effective than predicted so they removed em.

Andrea Kent


User currently offlineTdscanuck From Canada, joined Jan 2006, 12709 posts, RR: 80
Reply 14, posted (6 years 4 months 2 weeks 2 days 10 hours ago) and read 7853 times:



Quoting 6YJCX (Thread starter):
In the early 1980's I was on an Arrow Air DC-8 from NAS to MIA when the captain announced that we were a bit high on downwind to MIA 9R and that the vibration that was soon to start was the thrust reversers on the two inboard engines. I recall saying to my wife that this guy cant be serious, but he was. We were probably at fl180 or thereabouts coming up on the coast and within the next half minute or so were low and slow. How was this possible? It was not long after that when a Lauda Air 767 went down in Asia from tr deployment of one engine, according to accident reports and I often wondered if there were no lockouts to prevent this.

On the old low-bypass engines it wasn't a big deal. With the reverser out and the engine at idle the differential thrust isn't that big and is easily controllable. There isn't much impact on the lift because the reverser is under the wing and doesn't throw an efflux pattern over the wing.

Lauda was a disaster because it was a high-bypass turbofan mounted much farther forward and the increased inertia of the large spools meant the engine was still putting out appreciable thrust by the time the reverser deployed. That excess reverse thrust destroyed the lift over one wing. It was a failure mode that hadn't been fully assessed because it hadn't come up on most of the previous designs.

Since Lauda, a whole additional level of lockout was added to almost all T/R designs. Post Lauda, T/R's have three independant systems that all must agree before the T/R can deploy.

Tom.


User currently offlineFr8mech From United States of America, joined Sep 2005, 5098 posts, RR: 12
Reply 15, posted (6 years 4 months 2 weeks 2 days 10 hours ago) and read 7845 times:



Quoting Tdscanuck (Reply 14):
Lauda was a disaster because it was a high-bypass turbofan mounted much farther forward and the increased inertia of the large spools meant the engine was still putting out appreciable thrust by the time the reverser deployed. That excess reverse thrust destroyed the lift over one wing.

The re-engined DC8's are still permitted to use reverser inflight, even though they are high bypass. Though, as I understand it, here, even though inflight reverse is not prohibited, it is discouraged.

Another tidbit of information:

All 4 engines on a DC8 can go into reverse in flight. With gear handle up: #2 & #3 at anytime and limited to idle reverse. With the gear handle down: #2 & #3 have full reverse available and #1 & #4 have idle reverse available. Nose gear compression releases the gear interlock and makes full reverse available to all engines.



When seconds count...the police are minutes away. Never leave your cave without your club.
User currently offlineTdscanuck From Canada, joined Jan 2006, 12709 posts, RR: 80
Reply 16, posted (6 years 4 months 2 weeks 2 days 6 hours ago) and read 7809 times:



Quoting Fr8mech (Reply 15):
Quoting Tdscanuck (Reply 14):
Lauda was a disaster because it was a high-bypass turbofan mounted much farther forward and the increased inertia of the large spools meant the engine was still putting out appreciable thrust by the time the reverser deployed. That excess reverse thrust destroyed the lift over one wing.

The re-engined DC8's are still permitted to use reverser inflight, even though they are high bypass. Though, as I understand it, here, even though inflight reverse is not prohibited, it is discouraged.

Good point. I believe part of the issue with the 767 was that the nacelle is much farther up and forward, relative to the wing, compared to predecessor airplanes. As a result, the reverser efflux can go up and over the wing, destroying lift as well as causing drag.

Tom.


User currently offlineBlackbird From , joined Dec 1969, posts, RR:
Reply 17, posted (6 years 4 months 2 weeks 1 day 16 hours ago) and read 7698 times:

The exact amount of reversing power used on the DC-8 varies from model to model

IIRC, the DC-8-10 could use full reverse inboard, and idle outboard, the DC-8-20, 30, and 40 could use full reverse inboard, and 32 percent Max Continuous outboard, the DC-8-50's varied... not sure about the -60's.

To my knowledge the DC-8-70's were restricted to idle-reverse inboard. This is due to the fact the engines are mounted further forward and the exhaust can go over the top of the wing and reduce lift.

To my knowledge the load from the reversers is channeled through the nose-gear IIRC.

Andrea


User currently offlineFr8mech From United States of America, joined Sep 2005, 5098 posts, RR: 12
Reply 18, posted (6 years 4 months 2 weeks 1 day 15 hours ago) and read 7677 times:



Quoting Blackbird (Reply 17):
To my knowledge the DC-8-70's were restricted to idle-reverse inboard. This is due to the fact the engines are mounted further forward and the exhaust can go over the top of the wing and reduce lift.

To my knowledge the load from the reversers is channeled through the nose-gear IIRC

According to my reference material (the AMM) full reverse is available on 2 & 3 with the gear down. The inhibit is removed when the gear handle is put down. Nose gear compression removes the inhibit on the outboard engines and allows them to go to full reverse.



When seconds count...the police are minutes away. Never leave your cave without your club.
User currently offlineCedarjet From United Kingdom, joined May 1999, 7932 posts, RR: 54
Reply 19, posted (6 years 4 months 2 weeks 8 hours ago) and read 7580 times:



Quoting Airfoilsguy (Reply 12):
The Concord could use thrust reverse in flight as well, though I might be wrong.

No way. But the Trident, yes, they could deploy reversers in the descent (and did).



fly Saha Air 707s daily from Tehran's downtown Mehrabad to Mashhad, Kish Island and Ahwaz
User currently offlineMax Q From United States of America, joined May 2001, 4071 posts, RR: 19
Reply 20, posted (6 years 4 months 2 weeks 7 hours ago) and read 7563 times:

The Concorde was most certainly certified to use Reverse Thrust airborne.

There were no spoilers, they didn't do it that often but they could if they needed to.



The best contribution to safety is a competent Pilot.
User currently offlineDavid L From United Kingdom, joined May 1999, 9483 posts, RR: 42
Reply 21, posted (6 years 4 months 2 weeks 1 hour ago) and read 7544 times:



Quoting Cedarjet (Reply 19):
Quoting Airfoilsguy (Reply 12):
The Concord could use thrust reverse in flight as well, though I might be wrong.


No way.

You might want to take a look here at the comments of someone who knows through direct experience:

Reverse Thrusting In The Air--possible? (by 727LOVER Nov 17 2004 in Tech Ops)

And Reply 16, confirmed in Reply 26, here:

Use Of Thrust Reversers During Descent (by Tg 747-300 May 4 2002 in Tech Ops)


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