Boots and brakes

[Boac]

OK - will give it a 'public' go, then, if some are interested. My bit first:

Me, RAF QFI at the 'College of Knowledge', Cranwell. Student - capable young man but easily phased by a busy circuit, so in order to get him off solo I 'negotiated' with my boss to take him away to Hawker Siddeley (as it was then) Bitteswell, then a Vulcan and Buccaneer overhaul airfield, and VERY quiet. I had had a few jugs with the SATCO there while I was on an Air Cadet Gliding instructors' course, so he 'helped' with access/costs etc

Got Bloggs on his last circuit at Bitteswell before I sent him off to do his first top-gun' stuff. Partly to blame here with what happened as he flew his landing, since I was watching things that might kill me like airspeed, line-up, rate of descent and engine rpm, and did not notice that his feet had ridden up on the rudder pedals and he was applying full brake pressure as we flared to land (there is a triple pointer gauge low on the panel in front of the instructor showing master and L/R brake pressures which I always regularly checked on final).

A nice touchdown, and confirmation to me that he was 'ready', when I was thrown forward in my straps with a horrendous screeching noise from 'below' as the locked wheels skidded on the runway. What to do? Tyres probably about to burst, no maintenance at the field, might miss tea and crumpet in the Occifers' Mess at Cranners etc etc. Fortunately (late 60s), Woke/PC and all that guff was not yet in our order books, so I gave him a swift but firm karate chop with my left hand under his chin. This surprised him just a little , and his limbs 'withdrew' from all controls, releasing the brakes. I taxied the choking Bloggs off the runway and we 'debriefed'. He was pretty certainly not going to do that again, and to his amazement I told him he was going off solo AFTER I had checked for any flat spots on the wheels.... Good ol' Dunlop had done a good job and there was no problem, so off he went (and landed 'normally'...) .

I think he went on to be an excellent 'truckie', but I cannot remember.

[Fox3WheresMyBanana]

7 July 1986
https://aviation-safety.net/wikibase/138054
We were the junior course on 3 Sqn, 4 FTS, RAF Valley.
We'd just escaped groundschool for part of the day to get our helmets refitted by the doc*, and one of the guys was looking out the window on the Sqn, which was less than 400m from the threshold of the active.
Mark Cable's aircraft, on his second solo, had the left tyre burst on touchdown because the left brake was on, and the aircraft promptly veered off left, at which point my coursemate at the window shouted "Hey, look at this!"
We all turned and saw the aircraft leave the runway, the left undercarriage leg dig in, Mark eject, then the aircraft become a flaming cartwheel tumbling across the airfield.
The Crash Alarm went off for about a quarter of a second only. The local controller hit the alarm button promptly, but his brain had already worked out the wreckage was headed straight at him, and commanded his legs to start running in the opposite direction. So, his finger press was light and the button didn't lock in as designed.
The wreckage just missed the tower and ended up on the visiting aircraft area just in front. Slightly further down the same flightline were the aircraft of one of the other 4 FTS sqns (I can't remember which now). My friend Al was just about to lower his canopy and taxi. He looked at the marshaller to see that he had looked away (there was a possibility of the canopy det cord exploding when the canopy was closed in those days), to see the guy waving like mad and pointing behind. Al looked over his left shoulder, and saw the flaming cartwheel by now headed straight at him. He managed to shutdown, unstrap, and run so fast he actually catch the marshaller up before he was off the flightline. He still doesn't know how he did it. The wreckage stopped just a few tens of yards from his jet.

And there we were, watching it all from behind and thinking "This fast jet flying is serious stuff!".

Turned out that it was possible with Mark's small boot size, and only in the Hawk, and only in a strong crosswind, for his feet to be flat on the rudder pedals but still be putting some pressure on a toe brake.
So they redesigned the aircrew boot very slightly. I think Mark was back flying soon after, getting his wings with the rest of his course.

* Because of the 8G one pulled in the Hawk, the helmets needed to be fitted more exactly that they did for the Jet Provost, helmets being heavier in those days.
We also got our teeth rechecked by the dentist, because bits of the jawbone were the only body pieces reliably identifiable after fast jet fatal accidents.

[Boac]

Turned out that it was possible with Mark's small boot size, and only in the Hawk, and only in a strong crosswind, for his feet to be flat on the rudder pedals but still be putting some pressure on a toe brake.

Not with you there? Are you saying that Mark's toes were up on the pedals on landing? "Feet on the floor", old chap! You say "Flat on the rudder pedals"?? Was he taught correctly? That is what my lad did and look wot 'appened there!

[Fox3WheresMyBanana]

The Hawk rudder pedals are cupped. The back of the heel rests on the cup, rather than the cockpit floor.
It isn't possible to have the feet on the cockpit floor.

novo-cockpit-hawk-finlandia-foto-CMC.jpg (89.08 KiB) Viewed 601 times

The pilot's toes are therefore always over the toe brakes. I think I'm right in saying that as Mark kicked off the drift with right boot, his left boot was therefore bent enough forward to contact the left toe brake.
This had been anticipated in the design of both the boot and the pedals, but IIRC they added an extra, smaller, boot size later for guys like Mark, and didn't recheck the clearance.
This kind of thing gathered a lot more interest in the years immediately afterwards, partly because of this accident but mostly because of the introduction of female aircrew, who needed smaller sizes, and sometimes different shapes, in just about everything.

[Boac]

Design sounds a bit odd to me! Presumably you had special boots for the jet? In this pic are those the heel cups you mention? I cannot quite visualise how it is built. What are the horizontal bars?

[Fox3WheresMyBanana]

Thanks for the better picture.
Yes, the (normal) boot heels rested between the lower cup and the upper horizontal projections. These stopped your heels sliding off the pedals. You can see the toe brakes higher up.
I think the pedals were connected by a crosspiece, but that was further forward out of sight.

[drewdavis]

Useful information!

[admin2]

Welcome aboard to you, drew.

[admin2]

drewdavis - please check your private messages.

[reddo]

The Hawker (HS125) had a similar issue in that it had Maxarets, not ABS. So if you landed with your feet on the brakes, you'd end up with wheels locking up and the inevitable flat spot/tyre burst.
Since I had a true GA background, my feet were always firmly on the floor, however, a few of my colleagues weren't so blessed and thus a few flatspots happened.

[G-CPTN]

I am not familiar with aircraft braking, however I had considerable involvement with commercial vehicle braking as a design/development/testing engineer from Maxaret through to full electronic/pneumatic ABS.
Whilst Maxaret (as applied to trucks) was a simple (crude?) system compared to later (current) systems being 'slow' it's basic maxim was release and reapply of the brakes.
I cannot comment as it applies/applied to aircraft - maybe the response time was too slow?

I had much fun driving laden combinations (artics and truck/trailer multi axle vehicles) on genuine and artificial low-coefficient surfaces, including split coefficient.

A typical low-coefficient surface was watered smooth ceramic tiles - which became high coefficient if the watering failed!

My work taught me that ice with flowing water over it was the lowest coefficient naturally occurring surface - something that I confirmed in December 2022 as I slid down the steep highway outside my house despite wearing shoes with Commando soles and ended up in hospital with a broken shoulder - I used my right arm to break my fall!

[Boac]

Dredging deep into to the murky memory banks here, but I think Maxaret depended on wheel spin-up to 'set the scene', so landing with wheels locked...................

[reddo]

Yep, Maxarets needed spin up and if you'd left your feet "high" on the rudders, then you'd not get the spin up and cue a couple of tyres flat spotting/bursting.