BAC One-Eleven crash on test flight. Deep Stall
 

https://www.baaa-acro.com/crash/cras...klade-7-killed

Because this tragic accident occurred decades ago, few of todays airline pilots would have been aware of it. It is certainly well worth revisiting the accident report; particularly pilots currently operating T-Tail types.

I visited the crash site memorial a couple of months ago.

Very moving, especially with test flights out of Boscombe taking place overhead at the time.

https://cimg1.ibsrv.net/gimg/pprune....216fd28431.jpg

This:

https://www.aerosociety.com/news/aud...nnia-brabazon/

And other podcasts of interviews of Mr. Davies (kindly linked to me by another PPRuNer) have fascinating discussions of the stall testing of these types. Very well worth the listen!

I suspect that most pilots of T-tailed aircraft know why they have a stick-pusher.

Thanks for that link Pilot DAR. Absolutly fascinating.

1978 comments from Jock Bryce, from the One-Eleven website:

"All I could think of was that we had to tell those seven girls, the wives of the crew, before they heard it on the one o’clock news. But what could we tell them, since we had no definite news of the crew? I knew we couldn’t telephone them – we would have to go and see them. I arranged for each of the wives to have an individual visitor and meanwhile, I pressed for further information on the casualties. I had had no more when I heard the crash announced on the one o’clock news.

By 1.15 I had received the confirmation I dreaded – that all seven of the crew had been killed. When I rang Sir George Edwards I only got one sentence from him. “Never mind the plane,” he said, “look after those girls.”

I wonder what would have happened aerodynamically, if they had dropped the rear air-stairs...... if indeed they could be dropped in that flight regime??

Is it true - or just urban myth - that the TPs cooly transmitted their vain recovery efforts all the way down, to help further investigation/prevention?

Thoroughly enjoying the 747 lecture :ok:

I believe so.
The killer was that the "all flying" tailplane was servo tab controlled ( a bit like the Britannia's ailerons) i.e. the pilot had no direct link to the flying surface which basically just flew in the breeze. Lithgow went through a series of actions which he calmly recorded. These included applying max power, frustrated by the rate of descent causing the intakes to be stalled. There were a number of my Father's associates on board.
BAC sent a team across to tbe USA to explain to such as Douglas what went wrong.

BAC 111 Prototype
 

Very good coverage and investigation results in Brian Trubshaws book Test Pilot.
No doubt lack of fully powered elevator, and poss lack of appreciation of consequence of exceeding AoA limits rather caught out BAC with this.
IN fact industry as a whole was caught out with the T Tail stall situation as the Trident showed even after going in to public service.
Also Vickers had already T Tail experience with the VC10 which had not surprised anyone with its low speed handling at that stage.
As part of the ongoing 111 investigation trials were carried out on the VC10 with relation to airflow around the tail area at low speed.
It appears that the four engine configuration with associate wider engine beams provided an extra 'low set tailplane effect' on the 10 which helped to prevent pitch up.
Also the prototype 111 was not fitted with an emergency tail chute although the replacement test machine was.
Trubshaws book is really his Concorde story, but the earlier years of developing large machines including the Valiant, Viscount, Vanguard, 111.and 10 are a fascinating document in their own right, at a time when computers were not quite the slide rule replacement they became.

I recently read an accident report to a similar high tail type where the elevator used servo-tabs. I am unsure what type but fancy it may have been a DC9 or similar design. When the crew checked the flight controls before takeoff they all seemed to work normally. Except the only problem was there was no correlation between control wheel operation and elevator. Being servo-tab operated the elevator itself doesn't move if the aircraft is on the ground.

When the pilot pulled back to rotate nothing happened and the aircraft stayed on the deck. I forget the result but I think an abort was made too late to prevent the accident.

The cause of the problem started with high winds when the aircraft was parked overnight. The winds affected one elevator and forced it against its stops (?) and caused damage such that it wasn't connected anymore and merely floated free. It was not possible to see the problem during the preflight walk-around inspection. The other elevator was not affected but on rotation it didn't have enough lifting force to lift the nosewheel on its own. All the while the damaged elevator simply floated free during the takeoff roll. .

The above sounds like the Ameristar MD-83 at Ypsilanti in March 2017, though it would be more accurate to say that the elevator was completely jammed rather than able to float freely.

NTSB investigation report here: Runway Overrun During Rejected Takeoff

I always thought the original design had direct manual (cable) controlled elevators

Yes, the DC-9/MD-80 has manual pitch control, although it doesn't move the elevator directly, but moves the control tabs (or servo tabs, depending on which side of the Atlantic you're from).

BAC 111 Prototype elevator control
 

Surprising that BAC allowed this situation to go so far as it did, when other TP's who had flown the machine had already made adverse comments with regard to elevator authority and its lack of stability on landing. Even after the subsequent machines were modified yet another AC was written off at Wisley when the aircraft developed PIO on landing.
One would have thought the company took notice of what their TP's said !!!!

DC9
 

Iirc there was a hydraulic boost? Fitted to augment elevator control at low speeds..think it operated with full forward stick. The tailplane problem due to high winds was known and was clearly visible if you looked at it during walk around.

There was indeed a hydraulic boost, to provide more AND pitch than the servo tab could produce. See the 3 pages of description of the elevator control system in the accident investigation report I linked to in my previous post.

Became a maintenance instructor in 1966 anbd attended DC9-10 series school. Douglas was very aware of the problem. The DC9 did not have a "elevator boost control". Instead there was a "disagreement mechanism" so if the piloit was pushing the column forward but the elevators wer "UP", the hydraulic actuator operated and pushed the elevators "DOWN". In any noprmal flight configuration, the flying tabs did the work and the hydraulic actuator just went along for the ride.
Did the British authorities requie a "stick pusher" for the DC9?
DC9 had also installed "vortillon fences" under the inboard bottom of the wing and strakes up forward on the fuselage, all intended to aleviate deep stall tendencies.
I actually saw the TIA DC8 at JFK that had jammed elevators due to some tarmac paving breaking up and pieces flying up and lodging in the gap between stabilizer and elevator. I heard loud engine stalls and looked out the side window of a B727 I was troubleshooting. Saw the aircraft in an almost vertical position aand then fall off and go right down. Giant eruption of flame and smoke followed. Ghastly sight.

Back during my college days, we had a professor who talked about this BAC 111 deep stall crash (I'm guessing it was an Aero Stability and Control class but it's been ~45 years).
Anyway, after describing the crash deep stall characteristics that caused it, he stated there had been another flight test crash of a T-tail designed aircraft where they were simulating an electrical power failure that disabled the stick-pusher and inadvertently got into a deep stall. He even elaborated that they tried various tricks (that had been brainstormed after the subject crash) in an effort to get out of the deep stall, but to no avail. But looking on the internet - while I can find other deep stall crashes of T-tail aircraft - I can't find one that fits his description of happening during flight testing.
Anyone know what he may have been talking about?