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DC Sonic Boom/Citation Down in VA

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DC Sonic Boom/Citation Down in VA

Old 7th Jun 2023, 16:08
  #61 (permalink)  
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https://www.washingtonpost.com/trans...investigation/

[the pilot] was a retired Southwest Airlines captain and former member of its pilots union’s board of directors, the group confirmed. He had recently obtained the highest-level Federal Aviation Administration medical certificate and was rated to fly Boeing 737s, among other planes.

…[his] flight history… included 25 years and more than 25,000 flight-hours with Southwest. He also was certified as an aircraft mechanic
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Old 7th Jun 2023, 16:41
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Originally Posted by tarkay01
N611VG Was NOT a loss of pressurization By Dan Grader On YouTube

https://youtu.be/s0G9sthn8bU

This analysis by Don Gryder seems to make a lot of sense. Basically the pilot had a medical incapacitation ( heart attack, stroke, etc) early in the flight which none of the passengers noticed. On a loss of pressurization incident, the windows will fog over. This plane had clear windows. Basically, there was no copilot to take over when the pilot became incapacitated.

Dan covers all the salient points.
Or, for an alternative perspective:


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Old 7th Jun 2023, 18:17
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If it was not a cabin pressurization problem I would expect there would have been some very concerned people looking out the windows at the F-16s. Not to mention some cell phone activity and perhaps a pax in the cockpit trying to figure out how the radio PTT switch works.
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Old 7th Jun 2023, 20:58
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BFSGrad. I find it highly likely that a two-year-old would fall soundly asleep amidst the gentle hum and vibration of a relatively short airplane trip.

However, I’ve joked with others about the “baby barometer,” perhaps more applicable to infants, who have trouble clearing their ears and start wailing when the plane begins to descend.

I assume that one or both of the adults in the passenger cabin might have been checking their watches and the ETA as they were trying to go elsewhere upon arrival.

The lack of ATC communication happened extremely early into this trip, and we don’t know why, but hypoxia would go a long way to explain it. As to the passengers, per the Washington Post article I cited earlier, they’d known this particular pilot a long time and presumably weren’t strangers to the cockpit.

And yes, frost on the windows does reflect an abrupt loss of pressure at high altitude, not a slow leak. After all, when you hike up a mountain, the air gets thinner, but you don’t see your breath crystallize until it is really, really cold.

With a slow pressure leak, I assume the humidity from your breath in the cabin would leak away too, hence less to cause the windows to ice up.

PV = nRT. Pressure drop = temperature drop. Avogadro’s law. Ideal pressure law.

Pure speculation on my part.
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Old 7th Jun 2023, 22:24
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Useful update in the comments section of the video linked in post #62.

UPDATE: 6/6/23 ATC Audio Timeline:

1722:22Z N611VG checks in with Atlanta Center (ZTL) at FL230 and issued a climb to FL290 which was read back correctly.

1725:50Z ZTL issues N611VG a climb to FL340 as the aircraft was passing through FL277. This clearance was acknowledged and read back correctly.

1728:33Z ZTL amends the altitude to FL330 because of traffic in the next sector in Washington Center’s (ZDC) airspace. N611VG was passing through FL320. This transmission was never acknowledged and ATC was unable to contact N611VG again.

So somewhere between 1725Z and 1728Z (Shortly after takeoff, while climbing out) the event occurred that caused the remainder of the flight to out of contact with ATC. Jb.
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Old 8th Jun 2023, 23:28
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The guy in the video appears to have made up his mind already. They should have had a co-pilot is his unwavering view. To suggest the F16 action in intercepting a Zombie headed for DC was something to do with whose campaign he donated to tells you all you need to know about the commentator (and the US mindset).

An insidious depressurisation above FL300 will not fog out the cabin or freeze out the windows. An explosive decompression might.... But it will also have you going straight for your oxygen mask! I have done a few decompression test flights at altitude so I speak from experience. The passengers asked no questions of the pilot after the expected flight time had been and gone? Why not?
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Old 8th Jun 2023, 23:59
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Descriptions of the Comet depressurisations have the passengers suffer catastrophic physiological failure in next to no seconds. Wiki tells a distressing tale, deaths caused by ruptured lungs.
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Old 9th Jun 2023, 03:44
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Magplug:

Gryder specifically stated his opinion was the F16 action in intercepting the aircraft had nothing to do with politics or who the owner did or did not donate money to. He said the conspiracy theories had nothing to do with the accident.

Dan Gryder is definitely opinionated. We will find out in the future if he was correct in whole or in part.
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Old 9th Jun 2023, 09:28
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Originally Posted by Loose rivets
Descriptions of the Comet depressurisations have the passengers suffer catastrophic physiological failure in next to no seconds. Wiki tells a distressing tale, deaths caused by ruptured lungs.
Indeed so.

Though of course there is no suggestion that the Citation was subject to an instantaneous decompression.
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Old 9th Jun 2023, 10:33
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Originally Posted by what next
There are later Citation 560 models (the 560XLS and XLS+) whose autopilot has an automatic emergency descent mode. One prerequisite for that are electronically controllable engines (FADEC) which this 1990 model did not have, unless retrofitted at some later stage.
But there is a much easier and non-technical way by which some of these accidents, including the one over the Baltic Sea referenced above, can be prevented: Employ a second pilot. Money seems to have been no issue here, the aircraft owners could even afford to donate hundreds of thousands of Dollars to politicians. What are a few hunderd Dollars per flight in comparison to that?
Helios Airways Flight 522 had two proffesional, experienced pilots in the cockpit. That did not prevent death of everyone aboard.
I think that some automation might help - as already sugggested it is available on some more modern airplanes. And there is even emergency panic button for passengers available, that sends certain types of GA airplanes to automatic landing. (in case of pilot incapacitation, but passengers staying alert)
It seems there will be more single pilot incapacitation incidents in the future, as average age of pilots in those small jets goes up, methinks.
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Old 9th Jun 2023, 11:25
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Originally Posted by hoistop
Helios Airways Flight 522 had two proffesional, experienced pilots in the cockpit. That did not prevent death of everyone aboard.
We have had this discussion two pages up already. Of course there are plenty of examples of pressurisation related accidents that were not or could not be prevented by a second pilot on board. But there are many more happy outcomes due to an additional crewmenber. Not to talk about non-pressurisation related incidents that can only be recovered by a second pilot. Or, as you write, some kind of technical solution. There are some newer planes which can have this feature installed (e.g. Beechcraft Denali, Piper M600, Cirrus Vision Jet) but retrofitting an older aicraft like this C560 here is going to be a lot more expensive - if possible at all - than to pay for a second pilot for the next 20 years.
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Old 9th Jun 2023, 15:39
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Originally Posted by Magplug
The guy in the video appears to have made up his mind already. They should have had a co-pilot is his unwavering view. To suggest the F16 action in intercepting a Zombie headed for DC was something to do with whose campaign he donated to tells you all you need to know about the commentator (and the US mindset).

An insidious depressurisation above FL300 will not fog out the cabin or freeze out the windows. An explosive decompression might.... But it will also have you going straight for your oxygen mask! I have done a few decompression test flights at altitude so I speak from experience. The passengers asked no questions of the pilot after the expected flight time had been and gone? Why not?
DG is out with a second video that I find even less compelling. When he gets into his medical analysis, he wanders completely off the reservation.

There is a mindset that any decompression—fast, slow, explosive—will frost the windows. I agree that there is evidence that is not always the case; e.g., 2022 OE-FGR.

His medical (non-hypoxia) incapacitation theory hinges on the assumption that the two adult passengers would not have noticed the slumped-over pilot. While I’ve never flown in an older Citation, the few online videos from a cabin perspective show that the flight crew is clearly visible from the cabin. Seems unlikely that two conscious adults would not have attempted to render aid to the pilot and take action to address their urgent situation; i.e.. raise the cabin window shades, move to cockpit and start pushing buttons and twisting knobs. Then there’s the discussion of whether it’s technically feasible for a cell phone to make a connection from FL340.
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Old 10th Jun 2023, 17:48
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Originally Posted by MerrylParker
Dan Gryder is definitely opinionated. We will find out in the future if he was correct in whole or in part.
Sadly I don't think we ever will:

Gryder's assertion that the pilot was a fine upstanding union man with a spotless record has absolutely no bearing on his useful time of consciousness when experiencing a subtle decompression.

Captain Heffner may well have passed a class one medical yesterday but that does not reduce his chances of suffering a massive heart attack today. When I reached the age of forty it was mandatory to switch to a 6 monthly periodicity for UK class one medicals. I must have done two or three medicals like that. One day an RAF loadmaster aged in his late forties walked out of his medical and straight into a brief for a sortie. As he walked out to the aircraft 30 minutes later he dropped dead from a massive heart attack. It was at this point that the medical establishment reconsidered the validity of giving 6 monthly ECGs and the practice ceased. Now it is only mandatory for the over 60s.

We understand that there was no flight recorder on this aircraft and the dynamics of the crash simply left aluminium confetti. In the circumstances it seems very unlikely that any post-mortem evidence will be available to witness an explosive decompression. The Comet incidents mentioned above involved massive failure of the rear pressure bulkhead resulting in high speed loss of the empennage. That alone would have resulted in bodies being sucked clear of the aircraft and free-falling to earth around 120mph. Post mortem examination might have revealed at least some of what led to the death of the victims. A bizjet impacting at 29,500 fpm is quite another proposition. Therefore it seems unlikely that any evidence remains in this case that might witness the true cause of the crash.

There is a good reason that ATP pilots stop flying at the age of 65. It's nothing to do with the individual and all to do with balance of risk that comes with age.
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Old 10th Jun 2023, 23:01
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Originally Posted by BFSGrad
DG is out with a second video that I find even less compelling. When he gets into his medical analysis, he wanders completely off the reservation.
To be fair, Dan does give a pointer right at the start of the video - as he sits there with his "DTSB [geddit?] - Probable Cause" hat on - as to the likely value of what follows.
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Old 10th Jun 2023, 23:38
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Originally Posted by BFSGrad

There is a mindset that any decompression—fast, slow, explosive—will frost the windows. I agree that there is evidence that is not always the case; e.g., 2022 OE-FGR.
I think Dan Gryder is off the mark on this. “He doesn’t know what he doesn’t know.”

I’m not a pilot, but am a mechanic, with many year’s experience working on air conditioning and pressurization systems on small, medium and large jet aircraft.

A loss of pressurization at altitude will not (necessarily) inevitably lead to the windows frosting. It depends on what caused the loss of pressurization.

All jet aircraft use heated engine bleed air to condition the cabin air. In larger aircraft, that have a full ACM (Air Cycle Machine) the bleed air temperature can be modified to as low as 32 degrees F by using an expansion turbine combined with heat exchangers. (The bleed air cannot be pumped directly into the cabin from the engines as it is far too hot.)

The Citation 560 does not have a full ACM. Like many smaller GA jet aircraft, it uses bleed air and heat exchangers to set the incoming air temperature for heating. For cooling, (typically only needed on the ground on hot days, or at lower altitudes), it has a standard freon vapor cycle refrigeration unit, little different from a home or automobile air conditioner.

Larger aircraft, with a full ACM, can provide heated or cooled air (as needed) from a single unit.

Cabin air temperature will usually be automatically controlled by adjusting the mixture of heated bleed air and refrigerated air to keep the temperature at a comfortable level.

The incoming conditioned air is what pressurizes the cabin. The degree of pressurization is controlled by outflow valves, typically located at the rear of the pressure vessel, which permit the cabin air to discharge to the external atmosphere. On the ground, the outflow valves are fully open, and all incoming conditioned air flows right back out again, so the cabin pressure remains the same as external ambient air pressure.

Upon takeoff, the outflow valves begin to close under the control of the pressurization system, which permits the cabin air pressure to increase above ambient external pressure as the aircraft climbs. At high altitude, the outflow valves will be almost completely closed.

If a loss of pressurization is caused by a failure of the outflow valves - either because of a fault in the valves themselves, or the pressurization controller, (or failure by the pilot to enable the pressurization system in the first place), then the cabin pressure will drop to external ambient pressure.

But, in this scenario, the cabin temperature does not automatically drop to ambient temperature. The air conditioning system is still dutifully pumping heated bleed air into the aircraft. If the outflow valves are wide open, all that air is discharged to the external atmosphere so the cabin pressure remains at, or near external atmospheric pressure - but the air temperature inside the aircraft will not necessarily fall to ambient as long as a continuous supply of heated air continues to flow.

A pressurization loss caused by by a failure of the incoming air supply is another matter. In this case, the outflow valves might be working perfectly, and would quickly go fully closed, but with no incoming heated air, cabin altitude will rise to ambient, and the cabin temperature will quickly fall to extremely cold levels. The ambient air temperature at FL 340 is typically between -45 to - 55 Celsius (depending on the season).

In this scenario, the cockpit and cabin windows will likely frost over relatively quickly.If the cockpit windows are electrically heated, they might not frost up completely. If they are heated by the conditioned air supply (like an automobile defroster), they likely will frost up.

A third scenario is explosive decompression, which is anything that results in a major breach of the pressure vessel. That could be caused by a window or door blowing out, or structural failure of the pressure vessel. In this case there will obviously be loss of pressurization, and if the “hole” is large enough, even the best cabin air supply system would not be be able to maintain the temperature.

TL / DR

Pressurization failure caused only by a problem with the outflow valves will not necessarily cause cabin temperature to drop to sub-freezing levels, if the heated cabin air supply is otherwise working.

Pressurization failure caused by a total loss of incoming cabin air supply will cause the cabin temperature to fall to very cold levels quickly, with accompanying frosting of cockpit and cabin windows. Likewise for an explosive decompression event caused by a major breach of the integrity of the pressure vessel.

Jim Barrett
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Old 11th Jun 2023, 00:19
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An excellent and very informative post, JRBarrett. Many misconceptions are cleared and gaps in knowledge filled. Thank you!

- Ed
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Old 11th Jun 2023, 01:25
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Originally Posted by JRBarrett
I think Dan Gryder is off the mark on this. “He doesn’t know what he doesn’t know.”

I’m not a pilot, but am a mechanic, with many year’s experience working on air conditioning and pressurization systems on small, medium and large jet aircraft.

A loss of pressurization at altitude will not (necessarily) inevitably lead to the windows frosting. It depends on what caused the loss of pressurization.

All jet aircraft use heated engine bleed air to condition the cabin air. In larger aircraft, that have a full ACM (Air Cycle Machine) the bleed air temperature can be modified to as low as 32 degrees F by using an expansion turbine combined with heat exchangers. (The bleed air cannot be pumped directly into the cabin from the engines as it is far too hot.)

The Citation 560 does not have a full ACM. Like many smaller GA jet aircraft, it uses bleed air and heat exchangers to set the incoming air temperature for heating. For cooling, (typically only needed on the ground on hot days, or at lower altitudes), it has a standard freon vapor cycle refrigeration unit, little different from a home or automobile air conditioner.

Larger aircraft, with a full ACM, can provide heated or cooled air (as needed) from a single unit.

Cabin air temperature will usually be automatically controlled by adjusting the mixture of heated bleed air and refrigerated air to keep the temperature at a comfortable level.

The incoming conditioned air is what pressurizes the cabin. The degree of pressurization is controlled by outflow valves, typically located at the rear of the pressure vessel, which permit the cabin air to discharge to the external atmosphere. On the ground, the outflow valves are fully open, and all incoming conditioned air flows right back out again, so the cabin pressure remains the same as external ambient air pressure.

Upon takeoff, the outflow valves begin to close under the control of the pressurization system, which permits the cabin air pressure to increase above ambient external pressure as the aircraft climbs. At high altitude, the outflow valves will be almost completely closed.

If a loss of pressurization is caused by a failure of the outflow valves - either because of a fault in the valves themselves, or the pressurization controller, (or failure by the pilot to enable the pressurization system in the first place), then the cabin pressure will drop to external ambient pressure.

But, in this scenario, the cabin temperature does not automatically drop to ambient temperature. The air conditioning system is still dutifully pumping heated bleed air into the aircraft. If the outflow valves are wide open, all that air is discharged to the external atmosphere so the cabin pressure remains at, or near external atmospheric pressure - but the air temperature inside the aircraft will not necessarily fall to ambient as long as a continuous supply of heated air continues to flow.

A pressurization loss caused by by a failure of the incoming air supply is another matter. In this case, the outflow valves might be working perfectly, and would quickly go fully closed, but with no incoming heated air, cabin altitude will rise to ambient, and the cabin temperature will quickly fall to extremely cold levels. The ambient air temperature at FL 340 is typically between -45 to - 55 Celsius (depending on the season).

In this scenario, the cockpit and cabin windows will likely frost over relatively quickly.If the cockpit windows are electrically heated, they might not frost up completely. If they are heated by the conditioned air supply (like an automobile defroster), they likely will frost up.

A third scenario is explosive decompression, which is anything that results in a major breach of the pressure vessel. That could be caused by a window or door blowing out, or structural failure of the pressure vessel. In this case there will obviously be loss of pressurization, and if the “hole” is large enough, even the best cabin air supply system would not be be able to maintain the temperature.

TL / DR

Pressurization failure caused only by a problem with the outflow valves will not necessarily cause cabin temperature to drop to sub-freezing levels, if the heated cabin air supply is otherwise working.

Pressurization failure caused by a total loss of incoming cabin air supply will cause the cabin temperature to fall to very cold levels quickly, with accompanying frosting of cockpit and cabin windows. Likewise for an explosive decompression event caused by a major breach of the integrity of the pressure vessel.

Jim Barrett
C525, no ACM, bleed air used to directly pressurize the cabin with jus a heat exchanger in the engine mount. yeah, blew my mind too.
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Old 11th Jun 2023, 15:33
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Originally Posted by JRBarrett
Likewise for an explosive decompression event caused by a major breach of the integrity of the pressure vessel.
Not necessarily major. I think a failure of the pneumatic door seal would also do the trick.
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Old 11th Jun 2023, 16:56
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the F16 action in intercepting the aircraft had nothing to do with politics or who the owner did or did not donate money to.
If ANY plane violates Washington, DC, airspace without approval, it gets attention, especially if they fly over prohibited airspace.

Yes, this plane was too high to be within prohibited airspace, but it stopped communicating with air traffic control around fifteen minutes after takeoff, according to the newspaper. It certainly didn’t land at its planned destination.

The F 16 action may be due to concern about a hijacking, not who donated money to whom.

Last edited by visibility3miles; 11th Jun 2023 at 17:19.
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Old 11th Jun 2023, 17:14
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JRBarret - How much moisture is there in the heated engine bleed air?
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