2004 Pinnacle Airlines Flight 3701

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digits_
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2004 Pinnacle Airlines Flight 3701

Post by digits_ »

Another topic sparked some questions regarding the 2004 Pinnacle Airlines Flight 3701, the RJ that climbed to FL410.

I've encountered it a couple of times during various training sessions. The only info that is usually given, is the one in the wikipedia article: https://en.wikipedia.org/wiki/Pinnacle_ ... light_3701

I was curious as to what limitations they actually exceeded. I can't seem to find any factual information. The wikipedia article mentions that FL410 is a limit, which they didn't try to exceed, and refers to a recommended climb rate that was exceede, which again is not a hard limitation. Aerodynamically they managed to get it flying at FL410, albeit quite slow.

The problems started when the engines flamed out. Wikipedia mentioned they overstressed the engines. I'm wondering what happened there exactly. Did they put too much thrust on? Were the engines not certified for porlonged operation at FL410 and/or slow airspeeds?
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7ECA
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Re: 2004 Pinnacle Airlines Flight 3701

Post by 7ECA »

Here's the NTSB report:

https://www.ntsb.gov/investigations/Acc ... AR0701.pdf

Skimming the early pages;
During the flight, both engines flamed out after a pilot-induced aerodynamic stall and were unable to be restarted.
The National Transportation Safety Board determines that the probable causes of this accident were (1) the pilots’ unprofessional behavior, deviation from standard operating procedures, and poor airmanship, which resulted in an in-flight emergency from which they were unable to recover, in part because of the pilots’ inadequate training; (2) the pilots’ failure to prepare for an emergency landing in a timely manner, including communicating with air traffic controllers immediately after the emergency about the loss of both engines and the availability of landing sites; and (3) the pilots’ improper management of the double engine failure checklist, which allowed the engine cores to stop rotating and resulted in the core lock engine condition. Contributing to this accident were (1) the core lock engine condition, which prevented at least one engine from being restarted, and (2) the airplane flight manuals that did not communicate to pilots the importance of maintaining a minimum airspeed to keep the engine cores rotating.
Edit: It looks like this crew was an accident waiting to happen - at least they only screwed around without pax on board, mind you - but they were doing a bit of questionable maneuvering. Wanted to join the so-called "410 Club", an informal group at the airline, etc.
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Last edited by 7ECA on Thu Mar 12, 2020 5:19 pm, edited 1 time in total.
Ki-ll
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Re: 2004 Pinnacle Airlines Flight 3701

Post by Ki-ll »

It is my understanding that jet engines like undisturbed laminar air. During the stall of T-tail/rear engine airplanes air separating from the wing goes straight into the engines and causes a flameout. This also happened to a Tu-154 near Donetsk when the crew stalled the airplane in a thunderstorm at high altitude.
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pelmet
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Re: 2004 Pinnacle Airlines Flight 3701

Post by pelmet »

digits_ wrote: Thu Mar 12, 2020 4:59 pm Another topic sparked some questions regarding the 2004 Pinnacle Airlines Flight 3701, the RJ that climbed to FL410.

I've encountered it a couple of times during various training sessions. The only info that is usually given, is the one in the wikipedia article: https://en.wikipedia.org/wiki/Pinnacle_ ... light_3701

I was curious as to what limitations they actually exceeded. I can't seem to find any factual information. The wikipedia article mentions that FL410 is a limit, which they didn't try to exceed, and refers to a recommended climb rate that was exceede, which again is not a hard limitation. Aerodynamically they managed to get it flying at FL410, albeit quite slow.

The problems started when the engines flamed out. Wikipedia mentioned they overstressed the engines. I'm wondering what happened there exactly. Did they put too much thrust on? Were the engines not certified for porlonged operation at FL410 and/or slow airspeeds?
Just because your maximum certified altitude is FL410, it doesn't mean it is safe to go there. Going from memory of that accident, so can't guarantee all details are correct, they were too heavy for that altitude but wanted to get there anyways just to say they had been there(which shows in itself how rare it is for that type to get up there). If I remember correctly, in order to be able to get to that altitude, they had to climb at a speed which was quite slow. Their increased induced drag from increased AOA slowed them down. I think they noticed that they were getting slow but instead of just pushing the nose down to pick up speed(and therefore lower AOA) which would cause an ATC altitude violation, they wasted time getting a clearance and then stalled. A high altitude stall in a jet takes thousands of feet to recover. Their high AOA created turbulence which flamed out the engines and one got that core lock issue.

Never let yourself get too slow in jets like that up high. Your thrust is significantly decreased making it more difficult to power out of the increased induced drag situation and it can get to the point where there is not enough thrust to get out of the high drag situation. Then speed continues to drop. In terms of safety....overspeed(at least a bit of overspeed) is not a big deal, underspeed is a really big deal.
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Last edited by pelmet on Thu Mar 12, 2020 5:35 pm, edited 1 time in total.
digits_
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Re: 2004 Pinnacle Airlines Flight 3701

Post by digits_ »

Looks like the stall wasn't the issue in itself, but that stalling 4 times caused the dual flame out, which then was mismanaged and caused them to crash.

The part where the stall caused the dual flameout was the missing link I was looking for on the wikipedia page.
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pelmet
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Re: 2004 Pinnacle Airlines Flight 3701

Post by pelmet »

digits_ wrote: Thu Mar 12, 2020 5:32 pm Looks like the stall wasn't the issue in itself, but that stalling 4 times caused the dual flame out, which then was mismanaged and caused them to crash.

The part where the stall caused the dual flameout was the missing link I was looking for on the wikipedia page.
I suppose it depends on how you look at it. A stall in a jet like that is always a big issue in my opinion. And the effects of the aerodynamic stall led to the dual engine failure, probably something that was unexpected in a stall scenario. But they did recover from the stall to an unstalled condition. Really just one stall with multiple stickshaker/pusher activations
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iflyforpie
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Re: 2004 Pinnacle Airlines Flight 3701

Post by iflyforpie »

Climbing in vertical speed mode. Should have used flight level change which would have held an airspeed or Mach.

They got up to 410 on momentum, and were stuck on the back side of the power curve that the engines alone had no way of accelerating out of.

The plane stalled, and was stalled repeatedly by the pilots who didn’t perform a correct stall recovery, and both engines flames out.

The crew didn’t declare an emergency with a double engine failure, and they didn’t follow the correct procedures for a windmilling relight with resulted in both engines experiencing core lock due to contraction of the shroud/case around the turbine blades and insufficient airspeed to keep the cores rotating.

In addition, they exceeded temperature limits on both engines during the climb and brief cruise.

I think they could have easily maintained 410 if they were patient enough, used the proper autopilot modes, and monitored their instruments. I don’t know if the CRJ FMS will tell you which altitudes you can climb to but it might be good advice to follow it if it says unable 410.
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digits_
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Re: 2004 Pinnacle Airlines Flight 3701

Post by digits_ »

iflyforpie wrote: Thu Mar 12, 2020 6:40 pm
In addition, they exceeded temperature limits on both engines during the climb and brief cruise.
Do you have a source for that? I mean it sounds logical, but I can't find it in the linked document
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AuxBatOn
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Re: 2004 Pinnacle Airlines Flight 3701

Post by AuxBatOn »

There is generally a very specific climb profile to follow in order to make it to the service ceiling of the aircraft. Any deviations will result in either not reaching it or reaching it in a state where the aircraft cannot maintain its speed at max rated power (ie: with momentum, trading airspeed for altitude). It would be close to the subsonic portion of the Rutowski climb profile.

Stalling at high altitude is not a big deal. At least you have altitude to recover. Not following proper recovery procedures AND not following the engine restart procedures, or their indiscipline/incompetence is what killed them.

I have had engines stall on me at high altitude and slow speed (in the T-38. Engines have issues in certain regimes). Increase airspeed, maintain a minimum RPM on the motor, execute a windmilling start.
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pelmet
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Re: 2004 Pinnacle Airlines Flight 3701

Post by pelmet »

AuxBatOn wrote: Thu Mar 12, 2020 6:55 pm Stalling at high altitude is not a big deal. At least you have altitude to recover. Not following proper recovery procedures AND not following the engine restart procedures, or their indiscipline/incompetence is what killed them.
Thanks,

Just to clarify. I did say that stalling is a 'big deal' earlier but I suppose one needs to define what a big deal is and it would probably be defined differently for us.

First of all, at the company where I have been working, it you accidentally stalled an aircraft, you would be fired. A big deal for most employees. As well, flaming out both engines and damaging at least one of them and having an ATC violation obviously is an issue and the recovery could result in a traffic conflict. T-tail aircraft can get into deep stalls.

But I know what you are saying. You have probably done many pre-planned and perhaps not even pre-planned stalls at altitude. So I suppose when I say big deal...like almost anything, it depends on the context. So if you are a test pilot planning a high altitude stall in a big jet, perhaps no big deal...for an airline/business jet pilot, I suggest considering it a big deal.

I guess now I should look up the Rutowski climb profile.
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bobcaygeon
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Re: 2004 Pinnacle Airlines Flight 3701

Post by bobcaygeon »

iflyforpie wrote: Thu Mar 12, 2020 6:40 pm Climbing in vertical speed mode. Should have used flight level change which would have held an airspeed or Mach.

They got up to 410 on momentum, and were stuck on the back side of the power curve that the engines alone had no way of accelerating out of.

The plane stalled, and was stalled repeatedly by the pilots who didn’t perform a correct stall recovery, and both engines flames out.

The crew didn’t declare an emergency with a double engine failure, and they didn’t follow the correct procedures for a windmilling relight with resulted in both engines experiencing core lock due to contraction of the shroud/case around the turbine blades and insufficient airspeed to keep the cores rotating.

In addition, they exceeded temperature limits on both engines during the climb and brief cruise.

I think they could have easily maintained 410 if they were patient enough, used the proper autopilot modes, and monitored their instruments. I don’t know if the CRJ FMS will tell you which altitudes you can climb to but it might be good advice to follow it if it says unable 410.
The "Core lock" procedure didn't come out until after this event. This event initiated it. As already stated, they climbed too slow (below .7 mach id I recall) and couldn't get back "on the step" turning it into a big issue with further poor actions ie trying to recall from the stall too quickly causing the secondary stall. This whole event was a "Hold my beer and watch this" accident.
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Re: 2004 Pinnacle Airlines Flight 3701

Post by pelmet »

bobcaygeon wrote: Mon Mar 16, 2020 9:09 am ….. with further poor actions ie trying to recover from the stall too quickly causing the secondary stall.
True, a stall at low altitude that may be easy to power out of. But at same weight at high altitude can take many thousands of feet to recover from. After having lowered the nose, you are tempted to pull back on the control column to decrease the descent rate as the actual speed number looks OK and the red strips at the top and bottom of the ASI tape representing barber pole and stall speed appear to be far away from the current speed. But as soon as you start pulling with some g-loading, both red strips suddenly close the gap and move quickly toward your current speed and the stickshaker comes on again.....at least in the sim I was using.

Seems that a stall at high altitude in these kinds of jets requires an acceptance of many thousands of feet of altitude loss, so you won't be able to hide it from ATC. A Pan Pan(when appropriate) might be a good idea.
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Eric Janson
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Re: 2004 Pinnacle Airlines Flight 3701

Post by Eric Janson »

pelmet wrote: Thu Mar 12, 2020 5:21 pm In terms of safety....overspeed(at least a bit of overspeed) is not a big deal, underspeed is a really big deal.
I'd have to disagree - overspeed can damage the airframe. Any overspeed requires maintenance action. A stall will not damage the aircraft in any way.

Both cases need to handled correctly. At high altitude descending may be the only option to recover lost speed.
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pelmet
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Re: 2004 Pinnacle Airlines Flight 3701

Post by pelmet »

Eric Janson wrote: Tue Mar 17, 2020 5:31 am
pelmet wrote: Thu Mar 12, 2020 5:21 pm In terms of safety....overspeed(at least a bit of overspeed) is not a big deal, underspeed is a really big deal.
I'd have to disagree - overspeed can damage the airframe. Any overspeed requires maintenance action. A stall will not damage the aircraft in any way.

Both cases need to handled correctly. At high altitude descending may be the only option to recover lost speed.
Thanks,

I understand your what you are saying. Unintentional small overspeed events have happened to quite a few aircraft where I have been working over the years. It most often happens going into or out of a Jetstream in an area known for strong jetstreams where the windspeed can change quickly. Of course, it is desirable to avoid an any overspeed.

But....going from memory....The Mmo has a safety buffer(in fact I believe that the aircraft is designed to handle normally and is flight tested up to Vd, also known as design dive speed which is 10% above Mmo). Obviously, getting close to Vd/Md can be bad news.

As a reference for the reality that a small overspeed is not a significant safety hazard, here is another Airbus Safety First article on overspeeds which says...….

"In cruise, VMO/MMO provides a significant margin to design limits All Airbus aircraft are designed and tested to be safe to fly up to design limit speed, which is a value with margin well above VMO/MMO at cruising altitude."

"Inspection following an overspeed event
Aircraft inspection is only required when the speed exceeds VMO by 20 kt (or MMO+0.02 for A330/A340 aircraft and MMO+0.04 for A320 family). There have been no findings reported following inspections performed after overspeed events on Airbus fly-by-wire aircraft.
Management"

https://safetyfirst.airbus.com/app/them ... hp?p=23221

In all honesty, if I had to have one or the other, I'll take the situation of being briefly over Mmo by a couple of knots than a couple of knots below the stall speed where there can be a complete loss of control right away. Overspeed in cruise is typically just bring the power back(and possibly use speedbrakes depending on type) and then continuing on. Stall in cruise is big altitude loss, possible control loss, and in the case of the Pinnacle RJ...double flameout.

Personally, I suggest you reconsider your belief that a stall at high altitude is less worrisome than an overspeed.
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Last edited by pelmet on Thu Mar 26, 2020 6:42 am, edited 2 times in total.
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Re: 2004 Pinnacle Airlines Flight 3701

Post by valleyboy »

Little bit of a drift from the few above posts but certainly goes with over all thread. There a 2 real glaring mistakes I saw when people convert to jets. First flying above optimum altitude (especially in aircraft like Lears and in this specific case) and the other when asked to "expedite" climb or "best climb rate" and invariably the crew gets into a "zoom" climb and when the momentum stops your rate of climb drops to zero. When ATC made such a request when I was flying the answer was "roger" but the climb did not change. We were always at our best rate for A/C weight. When the steam runs out in a jet you are sucking the hind teat for sure. :mrgreen:
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pelmet
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Re: 2004 Pinnacle Airlines Flight 3701

Post by pelmet »

valleyboy wrote: Tue Mar 17, 2020 8:17 am There a 2 real glaring mistakes I saw when people convert to jets. First flying above optimum altitude (especially in aircraft like Lears and in this specific case)…..
Thanks,

Interesting comment about the Lears. Do you think they were more sensitive/unforgiving to flying above optimum than the typical airliner types. I suppose it depends on type. More than one MD-11 guy mentioned to me about stickshaker events in turbulence that were not particularly unexpected.

Manufacturers seem to like to make bigger planes with the same or almost same wing. Douglas did it with the change from DC-10 to MD-11 and Airbus did it with the 320 to 321 creating various problematic issues for flight crews.
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Re: 2004 Pinnacle Airlines Flight 3701

Post by rxl »

Every airplane, every situation is different but generally do not trade airspeed for altitude when up high ... say F340 and above. Stick to AOM climb profiles and abide by charted weight/altitude/temp/turbulence limits and be safe.
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