Looking at the vertical profile in post 47 I can’t really see how oxygen could be an issue.

Possibly CO, if they were just on airmix...but it also looks like the prop is feathered....

I don't think CO is a likely issue in turboprops, I've only ever heard of it for piston engines. Not sure about the exact layout of the exhaust and firewall, though.

The T-34C primary trainer that the Navy used for nearly 40 years had a for sure CO risk based on where the exhaust stacks were and the (abysmal) seal configuration for the sliding canopies. We had a NATOPS procedure for it and everything. Yes, it was A Known Issue.

For what it's worth, you could fly the T-28 (B and C) with the cockpit open - that was a recip with a powerful Wright Cyclone air cooled engine. Due to how and where the exhaust was configured, the pipes being a bit lower down and a bit further aft, you could have the canopy open inflight. My memory is somewhat foggy on that given how long it has been since I flew in a T-28, and I only recall one or two times that we flew with it open. We generally did not, however, when I was in training.
And before you ask: yes, we had electricity way back then.

@ all not familiar with the T-6 OBOGS war stories, and possibly the F-22 system and so forth........

Several incidents at Whiting field and other bases raised a flag for the Navy and USMC and USAF.

The problems that USAF and USMC are looking at is not low oxygen, but contamination. In the "old" days we had oxygen bottles and monitoring their health and well-being was easy. We didn't test at our mask connection for bad fumes or oxygen content or..... Hell one system I flew with had constant over pressure so I had pure oxygen unless I disconnected the nose hose. Apparently, the F-35 also has a slight over pressure, but I'll have to talk with one of the pilots( that feature was brought up during the accident investigation of a loss this past May here at Eglin).

The OBOGS was intended to reduce ground support issues and the oxygen tank weight/space/maintenance costs and effort. Sounded great, and I sit here now sucking on a home oxygen concentrator due to my poor habits for over 50 years. BFD!!! Trouble is the sucker doesn't work real good above 10,000 feet pressure altitude. The standard systems I flew with for a few decades had oxygen bottles and a regulator you could actually turn off or select emergency pressure. The OBOGS doofers do not seem to work that way.

https://www.navytimes.com/news/your-...-neighborhood/
Their names and a pic. Lots of questions here that need to be answered. I thought they had some kind of monitor now for contamination in the OBOGS? I would be so devastated if it were my daughter or son, R.I.P.

When we went through the only time the T-28 was flown with the canopy open was when doing circuits at the carrier or practicing same on shore at Barin (outlying field).


https://cimg2.ibsrv.net/gimg/pprune....2abc9300d5.jpg

30 miles might indeed be 48.28 kilometers but ABOUT 30 miles is most assuredly ABOUT 50kms

Some posts made about "push on ittis". I have not seen in the posts any comment on a mayday call being made. Surely if there was a problem there would have been a call. If not than it would seem reasonable to consider either a catastrophic failure, which would be substantiated by debris scattered over an area, or incapacitation.

In answer to keeping comments respectful, totally agree. Also on accidents being discussed in crew rooms, well this undoubtedly still happens, and not on this site, this is the bigger crew room.

@finest... et al...

The oxygen problem we are seeing is different than a simple lack of oxygen. Even if it was and not contamination, then you would not hear a MayDay call. You would see a smoking hole.

It was the same thing with our gee-loc crashes in the Viper back in the early days. No call, as the dude was unconscious. We had video recorders of our HUD and we also had a recorder in the seat to grab the last minute or so of flight conditions if we ejected. In other words, you could not lie to the accident board.

I just have this feeling that the crew became incapacitated for one reason or another and couldn't eject.

Megan there were at least two other fatals in our time.
A Vietnamese student entered the pattern at Whiting the wrong way the night before the accident you are talking about, became disorientated and lost control.
There was also one at the boat, VT5, during the period '66 - '67.

You know, of note, if those flightaware altitudes are correct and they were stable at 8000' initially, there is no pressure differential in the cockpit at 8000', the altitude where the pressurization system kicks in during a continued climb. There are various filters in the pressurization system. Are they active before a cockpit pressure differential is available?

I recall, even in the always unpressurized T-37 jet trainer smelling fumes at times (no not that) during various extreme maneuvering gyrations, momentary tail slide for example. The T-6 stacks are about in the same relative vertical position as the T-34, just a little further forward on the long nose, tail slide not required.

Even if you turn the pressurisation on after engine start,you generally have a `bleed` to the canopy seal, on most aircraft,although pressurisation will only start at some other altitude,ie 6-8k.,otherwise it gets noisy...and cold..

sycamore,

From further reading, you're entirely correct. :ok: There is an independent valve that routes bleed air for both the g-suits and canopy seal, which opens as soon as weight is off the wheels as long as the main bleed air switch is in normal. The separate pressurization valve begins to open around 7500', to maintain 8000' cockpit until a little over 3 PSI differential and then it climbs with the aircraft.

The unpressurized T-37 was noisy....and cold, particularly at 25,000'.

BTW, from what my family member T-6B & T-34C instructor tells me, in addition to OBOGS incidents, the T-6 has also had its fair share of G-LOCs.

(At some point, our family evidently fell victim to some Voodoo High Priestess' 'You will become a military Primary Instructor' Curse. :})

Good poop, Okie and syc I guess the pressurization profiles are close to what airlines use, i.e. 8,000 or so until "x" versus the old pressure differentials I grew up with. Have to review my Sluf manuals, but at 40K we had about 14K cockpit pressure. Our old schedule was about a 5 psi differential , so my Sluf numbers look about right. The 8K pressure is about 10 psi, and I live with that at my mountain cabin and used to go fish and hike and ski at higher alt - think 10,000 to 11,000 feet. So I guess the new folks in the b idness need more help than we had. Secondly, the oxygen concentrators like I use for COPD start to run out at 9,000 or 10,000 feet. So the OBOGS has to use bleed air, filter it, then get rid of the nitrogen and then....., or.... we could go back to the oxygen tanks most of us grew up with and all that would entail.

The local rags here in the Panhandle have several stories about the OBOGS complaints, and at one time some of the crews "went on strike", wrote letters and......

So I cannot rule out an OBOGS problem or another cockpit issue besides the oxygen system but maybe CO or other fumes. And I take it that the masks and regulators are similar to what we used in that you are not under pressure all the time and get ambient atmosphere plus oxygen until up around 25K, then get pressure.

The T-6 II uses a on-board oxygen generation system, or OBOGS that has had problems for a number of years. The AIr Force in 2018 undertook a "total rework of the OBOGS with a revised software package, and changes in maintenance routines, could take up to four years to fully implement – and there still might be more work to do afterward."

That quote is from the below article:

Air Force Says It Knows Why T-6 Trainers Are Choking Pilots, But It'll Take Years To Fix

Also from the article

“So far, technical efforts to date and analysis of data collected have determined that pilots have been exposed to significantly changing levels of oxygen concentration,” U.S. Air Force Lieutenant General Steve Kwast, head of AETC, said in a statement on Sept. 13, 2018. “The varying levels of oxygen concentration, even though in excess of what the body typically needs, has caused physiological stress that most pilots on most days actually adapt to without noticing.”

If they were down low it wouldn't be hypoxia per se, but it could be that they were getting "bad air" from the OBOGS that caused them to be impaired.

Impairment of the crew would explain no Mayday or emergency call on guard or Center (queue the indignant proper radio phraseology crowd argument here) and it would also explain the lack of ejection from such a high perch. I have no idea the Navy position on the Texan OBOGS but would bet they followed Beech's lead from the USAF fixes.

Thank you, Ugly

Whenever there is no "mayday" call, or any other call, it's CFIT or poor judgement when down low or incapaciation. And I have personally witnessed two gee-loc incidents in the early days of the Viper. Back seat for one and watched another in my flight for another.

I have to wait for the report like all of us, but I can't see some mechanical problem with the basic airframe or motor.

R.I.P. Guys

For Macho4050: while your kind sentiments are appreciated, they were both ladies.

I'm assuming he was using the word in a gender neutral manner where the fair sex may be referred to as "guys", common usage in some parts.