This was interesting, or at least I think so!

[Chock 17,769]

It's amazing what you learn about aeroplanes, and sometimes it is surprising how much you know, or can surmise with a bit of thought...

I was on the headset pushing out a Loganair Embraer 145 this evening. It was going off Stand 17 at Manchester, which if you know Manchester airport, is one of the stands in that weird little cul-de-sac near the old control tower. That bit of the ramp can get really busy at times, what with aircraft tails facing each other from three different directions and it being used by EasyJet, British Airways, Ryanair, FlyBe, Aurigny, Aer Lingus, Norwegian and Loganair, as well as having three baggage hall entrances for vehicles. When you drive around that bit, you need eyes in the back of your head. As such, when you push things off there, there are different procedures for which way you turn the aeroplane depending on whether it's a jet or a prop plane, but in either case you have to be careful not to start the engines too soon, owing to the blast from the engines potentially damaging vehicles or aircraft in what is a pretty tight and busy space, so I tend to have the aircraft pull well clear of stuff before allowing an engine start. This is actually a bit of a pain in the word not allowed if you push an A320 NEO off there, because the NEO's engines take ages to crank up and crews always want to start them up ASAP as a result of that slow start up, so you have to be pretty firm with them to stop them from doing that.

Now because it was dark and it is sometimes difficult to see the taxiway centrelines when in the tug, and because we were using a Mulag Comet to push it out, which is the smallest pushback tug we have; it's the one we use for Embraer 145s, ATRs and Do 328s (they are a bit weird to drive, they feel top heavy). So this meant the aeroplane ended up having to be cranked around in quite an unusual turn and then pulled straight onto the taxiway centreline up near Stand 43 before I was happy to allow the crew to start the engines without the blast from them potentially battering the rudder of a FlyBe Dash 8 parked on stand 16, especially since the Embraer's engines are mounted up fairly high.

So anyway, when the 145 was clear enough behind for me to be happy to let the crew know they could start the engines, I tell them they can crank up number 2 and then of course after that is at a decent N speed, I tell em it's okay to fire up number 1. By which time we're at the tug release point and so I ask them to set the parking brake and ask if it's okay to disconnect, they say yes, and so I tell them to hold position and await a visual confirmation on the left, then I disconnect the tug from the tow bar. I'm just about to disconnect the tow bar from the aircraft when they tell me they've got a problem, which is that their EICAS is showing RUD HDOV PROTFAIL (that's a rudder hardover protection failure caution message). So I ask them if they want me to reconnect the tug, but they say they can probably taxi back onto stand if they need to, but would I hold on just in case. So I say okay, I'll standby and I tell the tug driver to hold position and explain their issue to him, which is always a fun thing to do when you've got jet engines near you drowning out your voice and everyone's wearing ear defenders or headset phones lol.

So the Embraer crew contact the tower and report a possible issue, but before long they tell me the message has cleared off the EICAS and so they proceed. I ask them if they're sure it's okay and they say yes, so I disconnect everything, close and fasten the hatches, get clear and give em the wave off and off they go.

On the drive home from work I was curious about exactly why they'd get a message concerning the rudder which would then appear to sort itself out, although since it occurred when the engines were coming up to operating speed I figured I had a good idea why such a message might have popped up. But when I got home, I looked it up in the manual for the Embraer 145 and it turns out I was right about the reason, which is... If there is any disagreement between the FADECs or one engine is out, meaning you'd need more rudder authority, then hardover protection is disabled. So because the engines were still cranking up, the engines parameter signals must have had a bit of a moment where the FADECs disagreed, thus that message popped up, but when the engines smoothed out, the message cleared itself.

[Rbass 27]

Ya just gotta love computer airplanes 😉 In the old jets we had to think through solenoids, switches and valves. Now we have to think through software architecture. 

[himmelhorse 1,276]

Chock,

I did not get your response to my message to you due to the Moderator pulling the plug on the topic.

God to see you back and active mate.

Regards

Tony 

[FDEdev 955]

4 hours ago, Chock said:

...If there is any disagreement between the FADECs or one engine is out, meaning you'd need more rudder authority, then hardover protection is disabled. So because the engines were still cranking up, the engines parameter signals must have had a bit of a moment where the FADECs disagreed, thus that message popped up, but when the engines smoothed out, the message cleared itself.

A classic case of lack of system knowledge. You learn such things either through experience on type, or Captains usually are being told such 'specials' when they are doing their line training on the new type.

It was a big advantage that e.g. at JFK and IAD the guys on the headset were always technicians who knew the quirks of our aircraft. 

Edited February 8, 2020 by FDEdev

[Chock 17,769]

5 hours ago, Rbass said:

Ya just gotta love computer airplanes 😉 In the old jets we had to think through solenoids, switches and valves. Now we have to think through software architecture. 

Yeah, it's a bit of a double edged sword I suppose. I mean obviously it's good that the aeroplane has protection against some leadfoot giving it full rudder deflection at high speed, and also good that it makes an intelligent decision about binning that protection off if you are in a situation where you need lots of rudder at low speed with one engine out, although with the engines mounted up on the tail, I do wonder about just how bad asymmetric thrust could be on an Embraer 145. I guess the designers thought it could be bad enough to warrant it. But it kind of reminded me of when pilots were first getting used to all the fancy stuff the A320 had on it and were saying stuff like: 'why's it doing that?'.