Ask The Pilot

[Human]

If a four engined aircraft had to land with three operating at an outstation with minimal maintenance facilities, could it be signed off to take off with the remaining three engines?

Or would it be a case of repairing it in-situ regardless?

A very recent Air Crash Investigation was about a 3-engine takeoff which went horribly wrong. The episode name is “Deadly Departure” (season 24, episode 3) and it’s available to watch on 7 Plus for the next 9 days.

According to the episode, 3-engine takeoffs do happen every now and then. The episode is well worth watching.

 

[jb747]

If a four engined aircraft had to land with three operating at an outstation with minimal maintenance facilities, could it be signed off to take off with the remaining three engines?

Or would it be a case of repairing it in-situ regardless?

Three engine ferries certainly exist, but they aren't simple events, and have a nasty habit of ending up in the crash comics.

The failed engine would have to be made safe for the flight. The work for that could be just about anything, but would have to be approved by the manufacturer of the aircraft and the engine. Then the regulator of the country you're in, and the aircraft's home. And the airline would actually want to do it. Just as likely easier to fix/replace it.

But, if you actually wanted to do it, and the engine was made safe, any sensible regulator would want the crew doing the ferry to be specifically trained in the simulator beforehand. It would not be a case of the line pilots who are there doing it (back to the crash comics).

There are a number of issues. For a start, it's not a takeoff with the performance of 3 engines. It's quite a bit less than that.

If you line up, and spool up all three engines as you do normally, you will immediately depart the runway, and no amount of control input will stop the aircraft turning. The issue is that there is a thing called Vmcg, which is basically the minimum speed you need, to have enough rudder authority to be able to keep the aircraft straight after the failure of an outboard engine. That's quite a high number, in the order of 120 knots. So, the upshot of that is that your take off procedure will have to be bring up all of the engines to about 30% (that's the pause you always feel at the start of a takeoff), then taking the symmetrical pair up to TO/GA. Then bringing up the 3rd engine, but matching its power to about half of the rudder input. As the rudder isn't effective at less than 60 knots, there's quite a pause between the first pair being pushed up, and the 3rd moving at all. You can't take it all the way until you've passed Vmcg.

There's unlikely to even be a valid V1 (you cannot continue at any speed with another engine loss), and that's why no sensible regulator would ever allow it.

We used to have the occasional play with it in the simulator. In fact I've even done a single engined takeoff in the 767 sim. But it was done as an exercise in Vmcg, and lateral aircraft control, not as a procedure to actually be used.

I'm tipping with 3 engines operating it'll be able to fly to the nearest full service airport.

As long as you had a clean shutdown in flight, there'd be no pressure, or requirement, to land. Your range is reduced, but in many cases you could quite legally fly to your destination. A rough rule of thumb from the 747 was that within 2,000nm of destination, and as long as there was fine weather forecast, you'd most likely be able to continue.

 

[Hvr]

So, if you got to choose which engine failed is there a preferred side? Or inside v outside?

 

[QF WP]

Saw this on YouTube:

. Seems so easy when you have the explanation from a FI. For the pilots here, is this similar to your training for spin stalls?

 

[jb747]

Almost invariably in the sim any failure was an outboard, simply because that gave the greatest amount of yaw, and was hardest to control. For the same reason, when we practised two engines out, it was always on the same side. I can only recall one exercise where the failure was one on each side, and it was so easy that I could see why they never bothered.

There was no favoured side.

 

[jb747]

Seems so easy when you have the explanation from a FI. For the pilots here, is this similar to your training for spin stalls?

The CT4 wasn't allowed to be taken beyond an incipient spin (so before it stabilised). That still gave you about 3 turns. We didn't let go of the controls though. But you do have to ensure they're really central.

The Macchi, on the other hand, was allowed to be stable erect spun. And I guess it was very much like the video. I think we used to climb up to around 20,000' for the entry, and had to be out of it by 10,000'. As it's an out of control situation, it was a mandatory ejection if you passed 10,000 and it wasn't under control.

Things like the A-4 aren't spun, at least not intentionally. They can get very nasty.

Now look up inverted spinning, which is the same basic idea, but you're upside down. Extremely disorienting, but quite easy to enter from some aerobatic manoeuvres. Interestingly, whilst this was banned by the RAAF, the CT4 actually had a decent inverted spin (but nasty erect) and the Macchi, was the other way around.

 

[justinbrett]

Almost invariably in the sim any failure was an outboard, simply because that gave the greatest amount of yaw, and was hardest to control. For the same reason, when we practised two engines out, it was always on the same side.

Unfortunately the RAAF 707 tried this in real life (double asymmetric) and that resulted in the infamous line from the FE “well done sir, you’ve killed us all”.

 

[jb747]

Unfortunately the RAAF 707 tried this in real life (double asymmetric) and that resulted in the infamous line from the FE “well done sir, you’ve killed us all”.

Trying the real thing isn’t inherently dangerous, and the RAAF had done it forever in aircraft such as the C130 and P3. The problem was the way it was done. Starting at a speed slower than VMCA2, turning the rudder boost off, and rapidly increasing the power the power on one side whilst the other is at idle will not give a demonstration of anything other than a departure.

 

[ksksks]

There was no favoured side.

This is also true for piston twins with counter rotating propellors eg Duchess. For conventional piston twins (with clockwise rotating props), a left engine failure produces larger yaw and roll effects.

 

[Saab34]

With these strong winds seen in the Melbourne terminal area this week, are these captain only landings? Or do FOs operate these also?

Is there a gust limit on the TAF for FOs to conduct a landing?

 

[jb747]

With these strong winds seen in the Melbourne terminal area this week, are these captain only landings? Or do FOs operate these also?

Is there a gust limit on the TAF for FOs to conduct a landing?

There's a crosswind limit (15 or 20 depending upon how recently they checked out), but nothing beyond that from the company. It's up to the Captain. Looking at the TAF, I'd let the FOs land.

 

[AviatorInsight]

With these strong winds seen in the Melbourne terminal area this week, are these captain only landings? Or do FOs operate these also?

Is there a gust limit on the TAF for FOs to conduct a landing?

We’re allowed up to our max of 40kts on a 45m wide or greater runway (MEL). Our only restriction on FOs is operating into 30m wide runways (BNK, AYQ, etc) with a maximum of 10kts of crosswind.

I personally love the challenge of a good crosswind and am happy that there are some captains willing to let us fly it. Others don’t have the same confidence and that’s ok also.

 

[jb747]

The joys of crosswind. One of the more interesting ones to handle involves a relatively mild wind (call it 15 knots) that switches sides in the flare.

 

[MooTime]

So trusting most pilots enjoy the challenge of cross wind landing, nothing like a challenge to finish of a shift in any job imo?

 

[AviatorInsight]

So trusting most pilots enjoy the challenge of cross wind landing, nothing like a challenge to finish of a shift in any job imo?

Pretty much, the keyword there being most.

Yesterday's duty was PER-BME-PER-MEL. I operated the PER-BME and PER-MEL sectors (given to me by the Capt). Both had their challenges.

BME was 34° and only 10kts of crosswind but the ride was so bumpy and the speed all over the place due to the mechanical turbulence and hot conditions. I could the feel the back end of the aircraft fall out and gave the thrust levers a good workout at about 10ft to save the landing. Firm, yet right on the markers, so I was happy with that.

By contrast in MEL later on at about 2330 I still had 40kts of tailwind coming in from the West to join the GLS approach onto 34. That was a challenge itself as the aircraft tried to capture the localiser. As we went down the slope that wind reduced to only about 10kts and wasn't anywhere near as bad as the previous sector.

 

[Saab34]

Are crosswinds easier to land in a 737 vs say a single engine piston? Is it the same deal-e-o, ie hold aileron into the wind on touchdown?

 

[AviatorInsight]

Are crosswinds easier to land in a 737 vs say a single engine piston? Is it the same deal-e-o, ie hold aileron into the wind on touchdown?

Exactly the same technique. Crab into wind and then straighten up during the flare. I’d say the single engine piston is more advanced these days than the 737.

Momentum plays a big role for sure though. The Cessna 210 that was landing in front of us as we waited at the holding point was getting thrown around quite a lot in the same conditions compared to the A320 landing after.

 

[jb747]

There are a couple of different techniques for landing in crosswinds, and different aircraft will have their preferences.

Crabbing, and then pushing (NOT kicking) it straight at the end of the flare would be the most common. Smaller aircraft will also allow you to drop the into wind wing to counter the drift as you remove the crab. Large aircraft do not like wing down, so you need to ensure your crab removal doesn't happen too soon. I actually used to aim to remove half of it. Pretty much without exception, crosswind landings that go wrong do so because the drift is removed too soon. Better to land with all of it intact, than on the grass.

Some aircraft (747 and 767, and I assume other Boeings) actually allow landings with all of the crab intact, and this is the preferred method on a wet runway.

Aircraft like the A-4, you used wing down instead of crabbing, and simply landed it that way. You were also limited in how much aileron you could input (with the stick jammed against your leg), so the limit was only 25 knots.

 

[Seat0B]

So trusting most pilots enjoy the challenge of cross wind landing, nothing like a challenge to finish of a shift in any job imo?

As a pax in our Grumman Tiger, I HATE cross wind landings!

 

[Saab34]

What’s happens if you land in the crab?

I was on a remote flight once, I think it was a Cessna 210 or something, the young lad appeared to land in the crab, I recall we started drifting on touchdown (we went around after that), but not sure if that is a result of poor crosswind technique, or late applied straightening up. It wasn’t a pleasant experience.