Aircraft and tug part company

[XXTSGR]

HS, are you by any chance a tug driver? Because I get the very slight impression that Capt. S. is an ATR-rated pilot. He therefore probably knows the systems quite well. I get the impression that you're not quite a clued-up on the machine as you have led us to believe.

[Hand Shandy]

Sorry for the delay I`ve been playing with my tug.I`m perfectly aware of the hydraulic system architecture it`s written on 26vu in black and white [well green and blue so even old duffers like me can understand it], as for bringing up normal brake px thats routed via the crossfeed valve as you`d know , maybe i should have clarified, this will give you about 40seconds worth of brake use before px decays , although you may have hit the nail on the head if the brakeman was not trained correctly.Two incidents i`ve seen with aircraft deciding to go their own way have all been down to lack of hydralic pressure and not even size 10 safety boots would stop them . As for your comment captain that the aux pump is only there to just to take off the prop brake why have they designed it to run off the hot bat bus , to take the prop off you`d have to switch on the battery , a good idea from the French from a maintenance point of view , and if the small affair of an aux pump can repeatedly carry out undecarraige swings in the same time as an acw pump i`m sure it`ll stop a trundling ATR. It seems we`ve drifted from the original thread though as to why this happened .
Oh and xxtsgr both hyd pumps are of the conventional axial piston type , with a cylinder barrel containing 9 pistons the only difference being the flow rate of the acw is higher than the dc i learn`t that tugging around

[Clandestino]

ATR's "Both main hyd pumps loss" checklist calls for closing (or checking closed) hyd crosfeed, so after the landing gear lever is lovered, dc aux pump kicks in and gives you some pressure to lover flaps but gear goes down with a little help from gravity. There's warning in FCOM that in case of go-around you can not retract the gear, therefore it seems to me that opening crosfeed to pressurize green system by using dc pump is not ATR approved procedure, at least for flyers. I couldn't find the reason for it written explicitly in the FCOM but our French instructors told us that DC pump is too weak to supply both hyd systems.

[GotTheTshirt]

Irish Steve,
On large aircraft the shear pin will shear with any abnormal load not specifically steering turn limits.
In fact some tow bars can be used on different aircraft with different turn limits.
Many towbars have an interchangeable head so the bar can be used on different aircraft. I have used some tow bars that have a shear pin and then the head is connected to the bar with a steel pin in a slot. When the shear pin goes the head is still connected to the tow bar and flag is raised to show the shear pin has gone.
Another type that I have had shear on me had just the shear pin and when it sheared ( on an L1011) the head dropped on the tarmac and before the brake guy could react ( Moi ) ! the head dug into the tarmac and lifted the 2 nose wheels clear of the ground
Now whas that fun getting the nose gears back on the ground with no jacks

[Irish Steve]

On large aircraft the shear pin will shear with any abnormal load not specifically steering turn limits.

Correct. Even hitting a drainage ditch at the wrong speed and angle can take a shear out, I've seen it done several times, though it never happened to me. Where real care has to be taken is when one bar fits a number of aircraft, if the wrong bar is used, the shear pin can be too strong, and damage can result.

Very much the case with 767/777, where one bar fits everything from the 200 up to the 400 on the 767, and also fits the 777, as well as (If I recall correctly) the DC10/MD11/A330 and a couple of other heavies) Delta provided a couple of bars, identical to look at, one for the 767's and the other for the MD11. Use the MD11 bar on a 767-200, and damage can result, as the shear pin is just too darn strong.

Many towbars have an interchangeable head so the bar can be used on different aircraft.

Tends to be on the smaller aircraft, especially executive jets and small turboprops, where the head is the only thing that's different. I've not seen an interchangeable head on the larger jets. We had interchangeable heads for the Dash 8's, the 300 & 400 needed different heads, but the operator only provided one bar.

Another type that I have had shear on me had just the shear pin and when it sheared ( on an L1011) the head dropped on the tarmac and before the brake guy could react ( Moi ) ! the head dug into the tarmac and lifted the 2 nose wheels clear of the ground

Never come across one like that, and I'm not going to complain about it.

I think the worst bar I ever came across that I had to handle was an abomination that was provided to Dublin by Aeroflot for handling the TU154 aircraft. Due to the nose length, the bar was about 25 Ft long, and about 15" diameter, with a horrendously complicated hydraulic system in the middle that allowed the wheels to be used to connect and angle the bar so that it could be coupled up. Problems started when one of the tyres punctured, and went soft, and no one could do anything to repair it, and as a result, the bar became unstable, which meant it could fall over very easily. That did the hydraulic system no favours, and the end result was a bar that was a nightmare to tow, and even worse to connect to the aircraft and tug. Eventually, the problem was solved when another 154 operator "forgot" to take their bar on one trip, as theirs was much shorter, lighter and easier to use, as long as you could push in reverse, as with some of the tugs, it was too short to get the tug under the nose unless it was reversed in, so that the cab was still clear. Great fun if you knew how to push in reverse, a nightmare if you didn't <g> . The other bar that was a pig was the 747 bar we had, it was so short, trying to do a reverse push before a tow had to be done with great care, as it was very easy to get out of line, and because the bar was so short, getting it back in line wasn't always easy.


Biggest bar ever I never had to deal with, the flight crew always fitted and removed the bar on the AN124, it needed a winch to get it back in the aircraft, and they carried it with them, as it was so large and specialised, due to the double nose wheel. I did hear that it weighed in at about 5 tonnes, and after seeing it in use one day, I can well believe it.