Jim Barrett nicely stated

Not much.... that air can be several hundred degrees.

Time of useful consciousness at 28,000 (last reply to ATC at FL277) is about 3 minutes, which should be enough time to get on a mask. Less than 3 minutes later the pilot failed to respond to ATC. It's a coinflip between medical event or pressurisation failure.

Was the oxygen cylinder open? If not, was it in reach of the pilot? We will in due course hear from the NTSB.
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Not much at altitude. Even so, with a full ACM that can cool the air using a compressor driving an expansion turbine, there can be a significant amount of water that condenses at the outlet of the turbine, and which is removed by a centrifugal water separator. That is mostly an issue on the ground when the ambient air is very humid.

At altitude, the cabin air supply tends to be extremely dry. Many people tend to have sinus problems when flying for hours in a pressurized cabin. Some aircraft (primarily airliners) have systems to humidify the cabin air.

How much maintenance experience do you have on Citations? I ask because you are wrong on several points. Freon A/C is used to augment cabin cooling and is off at cruise. All Citations use an Air Cycle Machine during cruise for cabin pressurization and temperature control. I have 2,500 hours flying them.

See pages 2-51- 2-57 here

http://www.corporatejetsolutions.com...g%20Manual.pdf

CJ3 does not have an ACM....

We may be nitpicking here, but the CJ3 belongs to the the line of "CitationJets" which are all part 23 certified aircraft, whereas the line of "Citations", to which the accident C560 belongs, are part 25 certified and all of them have, among other differences, an air cycle machine. In my 3.500+ hours on Citations I have had two pressurisation issues so far. One was due to pilot error (because of "finger trouble" the pressurisation switch was selected to "Manual" when really the switch next to it should have been flipped - these things happen when switches are moved without looking) and the other was caused by a faulty outflow valve.

Because it has been mentioned above: 1) The cabin air at altitude is very dry because it always passes through a water separator. 2) A door seal fault is indicated by an amber warning light together with a master caution. There is a secondary (passive) door seal and even a failure of the inflated door seal should not result in a rapid decompression. 3) Some malfunctions of the air cycle machine will automatically switch the system to "emergency pressurisation" mode, which means that the cabin will continue to be pressurised with pure bleed air. Hot and uncomfortably loud (they say) but breathable. 4) The optional freon air conditioner is totally unrelated to the pressurisation system. It is electrically operated and can be used from the ground up to 18.000ft.

Required Equipment ???
 

I have never held a US ATPL or flown any jet smaller than a 737 so I am not so familiar with bizjets under US regulations....... Stop me if I get this wrong!

This CJ3 would have been operating under FAR Part 23 with a single pilot permitted by the MTOW being less that 12,500lbs and less than 10 passenger seats. Did I get that right?

FAR Part 23.1457 appears to require a cockpit voice recorder with the functionality described in Part 23.2500 ? Furthermore I don't believe this aircraft would be permitted to operate with a single pilot under any other worldwide jurisdiction (other than those few states that have decided to adopt FAA rules).

BTW.... That's not a question for the engineers !

Now serious allegations are being made against the pilot about on board usage of a drug Oxicontin an habit forming opiate used for pain. Post mortem may be able to throw some light on it.

No. MTOW for the CJ3 is 14K Lbs. We operated the CJ with 2 pilots, and an "SIC required" on the PIC license. All of us were trained as PIC, and qualified to fly as SIC.

Vilas please quote your source.

CJs, in later 3, 3+ and 4 exceed 12,500 pounds, but are still Part 23 SP planes. All require type ratings. This was a 560, derivative of the Citation II, with a Part 25 exemption

https://downloads.regulations.gov/FA...tachment_1.pdf

Didn't realize that was a difference between the C&CJ, and I am sure you know/remember more about it than I do, but I flew the Bravo/550 (with ACM) and the CJ3/525 (without) for 8 years & 4500 hours.
But if you want to have an FAA moment, read the MEL for leaking (optional) sink in the CJ lav. "secure door closed and put do not use sign on lav door". Copied straight from the C550 MMEL. But the CJ has the emergency exit in the lav in the back, and the Bravo has it up front. Regulations with holes you can fly an airplane through... (disclaimer, this was true in 2013, after 10 years in service, but maybe fixed 10 years later)

I think this is it. If you don’t like the article, I have it from several pilots who knew him that’s there’s a lot of fact in these accusations.

https://www.the-sun.com/news/8319382...repairs-crash/

Just a small note or two here...
Part 23 or 25 is the certification rules for the aircraft, not the rules they are operated under. That would be 91, or 135, or 121 etc. Even a 121 Airline has to operate under parts of 91.
Also, the 23.2500 rule would be for new aircraft after the part 23 re-wriite. The 560 is under 25, up to amendment 17, with a bunch of other rules at Higher amendments, depending on the aircraft SN
See rType Certificate Data Sheets (TCDS) - A22CE Rev 73
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Vilas I read the article and if true I will be surprised. I personally knew Jeff and while he had a temper, I find many of the accusations to be a stretch. I would also urge you to check the reputation of the us sun as it is reviewed to be tabloid reporting.
I will reserve judgement until the investigation is complete in any accident and will not utilize tabloids to attack any pilot’s character.
just my personal code of conduct.

I absolutely agree that The Sun is a tabloid, but their long article referenced above by galaxy_flyer includes the following quotes from the judge in a 2017 civil court case against his business partners that Mr Hefner lost:

"In his findings, Judge David Dugan wrote: "There was an abundance of testimony from McBride, MacDonald [...] of Hefner's improper conduct."Much of this testimony was actually corroborated by Hefner’s own testimony.

"These acts include but are not limited to changing locks on hangars and having improper airport access privileges denied to McBride and MacDonald to prevent them from accessing ICC’s business premises; removing and hiding property of ICC [...] denying McBride and MacDonald access to important tax and financial information.

"[And] Hiding aircraft owned by subsidiaries of ICC; pointing a gun at [MacDonald] and threatening the life of McBride and MacDonald on separate occasions; acting in a threatening and belligerent manner to employees of businesses with whom ICC did business; failing to maintain aircraft to an appropriate standard; and making improper unauthorized filing with the Florida Secretary of State’s office."

Hefner twice unsuccessfully appealed the decision.

He later filed for Chapter 13 bankruptcy on March 3, 2021.

The status of the filing at the time of his death remains unclear."




Wow ! It does look as if there is some explaining to come........

IB

If that back-story is true it opens new lines of enquiry for the NTSB team.

Isn't the First Amendment the very reason these tabloids can get away with saying exactly as they like? I choose not to read unsubstantiated tripe written in the gutter press..... it will turn you brain to mush!

First Amendment does not negate U.S. libel laws. Tabloids in U.S. are frequently sued for libel.

Article linked in post #94 looks to be well sourced. A basic tenet of public affairs is, if you know there’s negative information regarding your client, flood the media with a positive narrative first; i.e., the “Mr. Safety” stories.

I assume a CVR was not installed, so the investigation will have not much information beside the two F16 visuals and ATC recordings.