Here's a video from my phone a couple of days ago of a BA Airbus with a busted APU being started and pushed back off stand 42 at Manchester Airport. On such occasions (half an hour or so before this video commenced) the inbound aeroplane is listed on our systems as an 'FEP Shutdown' arrival, which lets us know that the aeroplane will taxi on stand, set its parking brakes, but leave the engine(s) running until someone (on this occasion it was me) has chocked the nose and then connected the ground fixed electrical power and signalled the crew that this is available. Then they will shut the engines down, thus ensuring they have electrical power even without a functioning APU and then everyone else on the ground can safely approach the aeroplane.

Because of this lack of an APU to provide compressed air to get the engine sucking air through for fan rotation and ignition, the aeroplane cannot start its engines when being pushed out without additional ground equipment in the form of the Fixed Electrical Power (F.E.P.) connection, and an 'Air Start' unit. On this video, the air start unit is out of shot off to the left, but the air line from it can be seen connected to the port underside of the aeroplane and you can hear the air start unit power up at around 9:40 in the video. Air start units are very loud because they are essentially a gas turbine engine similar to the APU in a jet plane, but instead mounted on a towable trailer. Typically what happens with an air start, is that all the ground equipment stays on the starboard side of the aeroplane, then the port engine is started, but it can be done the other way around, just so long as the engine which is started is not the one the person who disconnects the air line has to go near, for obvious reasons. There is a person placed in the road behind the aeroplane with marshalling wands to stop traffic from going behind the aeroplane once its anti-collision beacon is on, which can mean an air start can hold things up a bit at the airport, for ground service vehicles, however, on stand 42 (where this video is taken), there is a road behind the tug and so if you look at the windscreen reflection, you can see several vehicles make use of this option. Because people are a long way from one another and because of the noise levels, everything is done with hand signals, including signalling the person operating the air starter unit, who is given operating hand signals from the person on the headset, who is of course able to talk to the crew and so knows when they need the air to be cranked up and shut off for the start up of the engine without an APU.

When pushing an aeroplane back that has an engine running, there are two things to be aware of, first is that it needs a bit more throttle to push the thing, even when an Airbus engine is at idle, it still delivers quite a lot of thrust. The second thing to be aware of is where you maneuver the aeroplane in order to avoid blasting people or vehicles with the thrust coming out of the engine, since this can be felt pretty strongly up to about 200 yards away. My concern on this pushback in this regard, was the EasyJet Airbus on Stand 1, the passenger bus near to it, and the Loganair ATR-72 on Stand 17, so you can see that I deliberately aim the back of the aeroplane so as to avoid blasting any of these too much, and I also don't push the aeroplane too far past the taxiway centreline for the turn onto taxiway Juliet Foxtrot (the one where we finish up), since this turn is designed to be far enough away from most stuff to not have jet efflux blast things too much from aeroplanes taxying alone this route.

You will also notice that the second engine is not started until the aeroplane is at the Tug Release Point (TRP 44). This is because with the thrust of one engine being used for crossbleed air to to crank the other engine, you would typically want the ground service equipment (tug/bar) off the aeroplane before applying that much thrust; it is in fact usually an airline S.O.P. to do that. Strictly-speaking, the MAG tug manuals (which are in each tug) have it that you would normally start the engines at TRP 44 anyway for a push off that stand, but most people on the headset (in this video that's my work colleague Sam), use some common sense and let the crew start cranking stuff the moment the tug is pulling forward and straight, and they have ensured there is plenty of room behind the aeroplane, so that's usually a few yards before the nosewheel actually gets to TRP 44. This is especially true with A320 NEOs and 737 MAXs (not that this is one of these in this video), since these have engines which take a long time to get up to stable operating speeds.

Fun jet plane fact for this video: If you look at the inboard side of the engine cowlings on this aeroplane, you can see a small fin sticking out of the top half of the cowling directly above the engine intake warning decal. If you've ever wondered what that fin is for, what it does, is direct air over the top of the wing to directly behind the engine pylon. Without that fin to steer some air around the engine, the engine would be blocking the airflow to the top of the wing.

If you want to skip the boring bits, the air start commences at 9:40, the pushback commences at about 18:00 after an Aer Lingus (Emerald) ATR-72 gets onto the stand opposite, but for those of you who like listening to ATC operations, the ground frequency at Manchester is on all the way through the video, since tug drivers have to monitor this frequency.

This was lunchtime on a Saturday toward the end of the mad morning rush where there is then a bit of a lull in operations for an hour or two (not for me, I went straight over to the opposite stand after this push and worked on that Aer Lingus and headsetted that one out, then went over to that Loganair EMB-145 you see on stand 18 in this video, and pushed that one out as well (and that one needed an air start too). The Loganair ATR-72 you see on stand 17 which I was avoiding blasting with the Airbus engine on this pushback, had earlier been pushed out for a departure, but it was unable to start its number one engine, so had been towed back on stand, but about twenty minutes after this video, it was towed off to one of the remote stands to get it out of the way (I think it went to Stand 67)  So you can get an idea of how it goes at that time at EGCC where operations are concerned and the fact that I did two pushes of air starts in the space of about half an hour or so, tells you that if you like simulating some system failures on your aeroplanes, in particular the APU, such failures are reasonably commonplace on aeroplanes which get used a lot:

For those of you who like to manually do your own pushbacks in the sim, the trick is to watch the tail of the aeroplane and get that to curve at such a rate of turn that you know it will end up going down the centreline, since if that happens, the main wheels will have to end up straddling the centreline and the nose wheel will end up on the line too, unless you want to turn it with a subsequent pull forward (as is the case here), where the thing to do is to just use a bit of common sense about placing it to best make a turn. When reversing, the trick is to simply keep the tug straddling the line and the plane will then have no problem going down the line too, them when you see the tug go over the TRP, you ease off the throttle and let the tug and aeroplane coast to the TRP and a soft touch of the brakes will be enough to stop things without jolting the passengers around.

 

Edited July 11, 20223 yr by Chock

Very interesting! I once watched a Delta 747-400 being started this way at the gate in KDTW. They started one engine at the gate on the ground air cart (it was number 3 as I recall) then pushed back to start the remaining engines via cross bleed.

I work for a corporate operator of 3 CRJ-200s. We have no ground air cart available at our airport, so we purchased a “buddy hose” which can be connected to the bleed air manifold of one CRJ to supply pressure to start one engine of the second aircraft with an inop APU. They have to be tugged into position side-by-side to do this. We have never had to do this operationally, but we do practice it once every 12 months so all our mechanics and pilots remain current on the procedure. 

We have had several instances of APUs that could not be started during descent - usually due to a “APU DOOR INHIBIT CLOSED” CAS message. As you may know, the APU door actuator on the CRJ-200 is a piece of junk, so this is not uncommon. When this happens at an away airport, the pilots have to keep the number 2 engine running at idle on the ramp, while passengers and baggage are unloaded/loaded. Since we operate primarily at FBO facilities, the crew will call ahead on ARINC to alert the FBO in case they need the aircraft to park at a specific place on the ramp with a running engine.

We have not (yet) had an APU fail unexpectedly after engine shutdown at an away airport with no ground air cart, but if that did happen, we would have to dispatch one of our other CRJs to the airport with mechanics and the “buddy hose” to do a “jump start”.

We did have an Allegiant A320 a few weeks ago whose APU shut down unexpectedly after parking at the gate, and it could not be restarted. (Apparently the ECU failed). They tried to arrange for a ground air cart to be trucked down from Rochester (KROC) which is a 2-hour drive away, but for some reason that was not possible, so they had to remain overnight. Another Allegiant flight arrived the next day with a replacement ECU and a mechanic to install it.

Delta used to have a ground start unit based at our airport for their CRJ700/900s out of Detroit. For some reason they removed it several years ago. This was not an “Mobile APU” as you used, but a big air tank on wheels with a diesel-powered air compressor attached. When fully charged the tank could supply 40 psi at sufficient flow rate for long enough to start an aircraft, but if for any reason the start attempt was unsuccessful, it would take about 15 minutes to recharge the tank for another go.

Edited July 11, 20223 yr by JRBarrett

Same procedure we used at US Airways\ American. We would airstart one at the gate and they would have to crossbleed to start the second engine after pushback. Some pilots would get irate when you wouldn't let them start both engines at the gate. Sorry sport, it's a safety issue.

8 hours ago, JRBarrett said:

As you may know, the APU door actuator on the CRJ-200 is a piece of junk, so this is not uncommon...

I've only ever worked on the slightly larger CRJs, typically SAS and Lufthansa ones (900s and 1000s), but I do know that with its origins being basically an enlarged private jet, the CRJ does suffer from not having stuff which is of the typically robust nature of the things you usually find on airliners. Among these, the towbar connection is not the best and the access door for the FEP and the headset connection isn't brilliant either. The engine nacelle placement doesn't leave a ton of room for clearance of the safety rails on belt loaders when accessing the rear cargo hold, such that some of these cannot even be used on the type. It's not a bad aeroplane, but as I say, it does betray its private jet origins somewhat. If you compare it to the Embraer 145 and 135, which would probably be its most similar analogue among airlines, that thing is a bit better in these respects, although the cargo door on these, whilst pretty robust, seems to have been designed to be as convoluted a mechanism as is possible, unless we consider the Embraer 170/190 series, which also has a ridiculously convoluted pair of cargo door mechanisms that never cease to make life harder than it needs to be.

1 hour ago, Chock said:

I've only ever worked on the slightly larger CRJs, typically SAS and Lufthansa ones (900s and 1000s), but I do know that with its origins being basically an enlarged private jet, the CRJ does suffer from not having stuff which is of the typically robust nature of the things you usually find on airliners

The 200 is closest to the parent Challenger 600 in terms of the switches in the overhead panel for things like bleed air management and fire systems tests. Those were greatly improved on the 700/900/1000. The APU on the 200 is actually quite robust - it’s just the air inlet door that is poorly designed.