Ask The Pilot

[Quickstatus]

When the aircraft is in trim, you can let go of the controls, and it basically sits where you left it (as long as the speed and power don't change)....
...Aircraft that are a little bit bent (which is most of them) will normally need a slightly different roll trim setting at different speeds.

Why just roll (which would be the ailerons?)and not pitch (stabilisers?) or yaw (rudder?)

 

[jb747]

Why just roll (which would be the ailerons?)and not pitch (stabilisers?) or yaw (rudder?)

Pitch will always change with speed variation. Go faster, tail makes more (negative) lift, and you'll need nose down trim. Go slower and the reverse happens.

In piston engined aircraft, much the same thing happens. The vertical tail is mounted at very slight angle, largely to account for the slightly crosswise air flow that's caused by the propellor. So, at different speeds, and power settings, you'll need different rudder inputs. Jet aircraft don't have this effect, and additionally they are invariably fitted with yaw dampers, which tend to remove any small effects in yaw. If you have an engine out, you'll be back to trimming the rudder for each and every power setting and speed.

On a straight, and properly rigged aircraft, roll inputs should normally be in balance. A change in roll with speed tells you that the wings are slightly 'different'. That could be caused by the flight controls not settling into exactly the same positions, or the whole aircraft could be very slightly twisted. Even slight variations will become evident.

Airbus masks all of this behind the FBW, but it becomes very evident if you have a law change that removes the autopilot. Then the ailerons will remove any trimming input they've been providing, and go to a faired position. The one time I saw this in the aircraft, almost a quarter of aileron input was required to hold wings level. The lack of trim means that you cannot trim out this loading, and have to keep the input applied for the remainder of the flight. A way around this exists to a degree, as the secondary effect of rudder is roll, so by using the rudder trim you can balance a moderate roll input, but at the expense of flying slightly sideways. It's dumb that provision for roll trim isn't provided.

 

[Quickstatus]

Presumably degraded law and non autopilot flight would not be a normal situation in current day commercIal operation - you would not fly QF93 in its entirety in non autopilot law

However in other circumstances maintaining such input would be tiring if unable to trim?

So OJH needed the least trim of the 747 fleet?.

 

[jb747]

Presumably degraded law and non autopilot flight would not be a normal situation in current day commercIal operation - you would not fly QF93 in its entirety in non autopilot law.

Far from normal. It was the early days of the aircraft. Basically it lost an air data computer, followed about 3 hours later by the loss of the probe heat on another ADC's sideslip probe. The aircraft saw that as a dual ADR failure, and reverted to alternate law II...basically no automatics. In that instance it was flown on for another 4 hours, as that was seen as the best flying outcome. Weather at the closest alternatives wasn't all that nice, whereas continuing meant the approach would be in daylight, and somewhat better weather. The flying roster was 10 minutes per pilot...very tiring. So, no, you wouldn't dream of continuing across the Pacific, but you'd always balance the issues of flying a degraded approach to an alternate, versus continuing (even if to different alternate).

However in other circumstances maintaining such input would be tiring if unable to trim?

Flying an aircraft that is out of trim, in IMC, is very undesirable. A partial fix, via the rudder trim, made it much more reasonable.

So OJH needed the least trim of the 747 fleet?.

That's how I remember her....

 

[WheelieBagWanderer]

Hi JB,

Regarding the the MH A330 that diverted to ASP yesterday (seemingly on one engine according to passenger accounts) flying the SYD-KUL sector, Flight Radar 24 shows it turned around over BME and headed back to ASP.

It looks to me that DPS is slightly closer to BME than ASP. Given than Garuda has a large A330 fleet and therefore technical assistance and maintenance personnel qualified on the A330 and many more accommodation options than ASP, wouldn't this have been the best spot to head to?

Or is there a stipulation that a decent-sized body of water cannot be crossed when flying on one engine in a twin-engine aircraft? If no stipulation would the captain potentially have felt more comfortable flying over desert rather than water?

Any thoughts on why he turned around and went to ASP?

 

[jb747]

Regarding the the MH A330 that diverted to ASP yesterday (seemingly on one engine according to passenger accounts) flying the SYD-KUL sector, Flight Radar 24 shows it turned around over BME and headed back to ASP.

It looks to me that DPS is slightly closer to BME than ASP. Given than Garuda has a large A330 fleet and therefore technical assistance and maintenance personnel qualified on the A330 and many more accommodation options than ASP, wouldn't this have been the best spot to head to?

Garuda may have plenty of 330s, but that doesn't mean there's a great deal of support at Bali. They will be capable of minor maintenance, but just as likely they'd fly in people if they needed to do more.

In any event, neither accommodation nor maintenance capability should be a factor after the loss of an engine on a twin. All other things being equal you should land at the nearest airport capable of safely operating that type. Not necessarily the nearest airport, but one from which the aircraft could operate in normal circumstances. Broome is close to equidistant from Learmonth, Darwin, and Bali, with Alice being about 100 miles further. The likely winds would actually mean that flight times would be very similar. Of the bunch, Darwin is the best choice, but its weather forecast included thunderstorms, which is a valid reason not to consider it.

There is also one closer airfield that doesn't normally get mentioned, but which is quite capable of handling an A330. RAAF Curtin.

Or is there a stipulation that a decent-sized body of water cannot be crossed when flying on one engine in a twin-engine aircraft? If no stipulation would the captain potentially have felt more comfortable flying over desert rather than water?

Not at all. You're not going to safely end up in the water or the desert, so there's nothing to choose between them.

It would be interesting to hear the radio conversations. You might glean a bit more from that.

 

[AviatorInsight]

Further on from that, I’d much rather stay in Australian airspace than continue on to Bali. At least having one of the parties that speaks English as their first language would make a difference. I’ve had to turn around back to Australia whilst in Fijian airspace and that was a debacle, good thing it wasn’t a full blown emergency.

Just curious JB, like in all the Boeing checklists for OEI ops it mentions “plan to land at the nearest suitable airport”. Does the same exist on the Airbus?

I do also agree that the nearest physical airport may not necessarily be the best option. But considering that they may not be familiar with Australian airports and they had flown over ASP just before, that was just an easy decision for them?

 

[docjames]

Graphic representation above.

Depending on how far south of BMW, then ASP may have actually been closer <redacted - jb has already answered>

• BME ASP 120° (SE) 118° (SE) 856 mi
  BME DRW 058° (NE) 056° (NE) 691 m

I'm surprised BME isnt A330 capable.

 

[cmon0005]

Regarding the the MH A330 that diverted to ASP yesterday (seemingly on one engine according to passenger accounts) flying the SYD-KUL sector, Flight Radar 24 shows it turned around over BME and headed back to ASP.

It looks to me that DPS is slightly closer to BME than ASP. Given than Garuda has a large A330 fleet and therefore technical assistance and maintenance personnel qualified on the A330 and many more accommodation options than ASP, wouldn't this have been the best spot to head to?

Or is there a stipulation that a decent-sized body of water cannot be crossed when flying on one engine in a twin-engine aircraft? If no stipulation would the captain potentially have felt more comfortable flying over desert rather than water?

Any thoughts on why he turned around and went to ASP?

I preface that I have no expertise in anything this is just a layman's observation, why wouldn't they have landed in BME? the runway is about 100m longer than ASP, if it were an emergency surely BME would be a good choice?

 

[jb747]

Further on from that, I’d much rather stay in Australian airspace than continue on to Bali. At least having one of the parties that speaks English as their first language would make a difference. I’ve had to turn around back to Australia whilst in Fijian airspace and that was a debacle, good thing it wasn’t a full blown emergency.

I've seen that go both ways. Aussie ATC yabbering in my ear about things I didn't care about, whilst flying a single engine approach, vs Manila who were excellent. Even a fairly complex diversion in India/Yangon worked pretty well.

Just curious JB, like in all the Boeing checklists for OEI ops it mentions “plan to land at the nearest suitable airport”. Does the same exist on the Airbus?

Airbus have two comments that they add to the ECAMs. Land ASAP...which means you might die if you don't. And Land ANSA - at nearest suitable airfield.

I do also agree that the nearest physical airport may not necessarily be the best option. But considering that they may not be familiar with Australian airports and they had flown over ASP just before, that was just an easy decision for them?

I expect that's very much the case. But, it's always worth remembering that you don't have to stick to the original plan. Even after turning towards Alice, the option to go to Curtin existed for quite some time. Their FMCs may not have had the GPS approaches available, so perhaps the idea of a single engined, non precision approach, to a place they've never heard of, didn't appeal.

 

[jb747]

More than just runway length, makes a runway suitable or not.

Emergencies come in many forms. Some are so dire that you'll be happy to just get the aircraft down, and don't care if it never flies again. It's not inconceivable that you'd consider going off the end of a short runway at 50 knots to be a good outcome, compared to flying for any longer.

Most emergencies aren't that bad. So, whilst you can't continue the flight, you don't want to damage the aircraft, or its contents, or anything on the ground. In that case you need to pick a runway that is suitable for the normal operation of the aircraft. Whilst a runway might be long enough, it may not be strong enough for your aircraft type. Taxiways, may not be wide enough, or strong enough. If you can't get off the runway, you've just closed the airport.

As far as I know, the largest aircraft to service Broome is the 737. Curtin, on the other hand, has to deal with the RAAF's C17s and A330s. But, it's unmanned, and in the middle of nowhere.

 

[Major]

RAAF Base Curtin - Wikipedia

 

[Heater79]

Send up a business card, or tell the cabin crew.

JB, when you're made aware that someone from this board is on one of your flights, what do you do? (Or try to do?) Do you head down to say hi?

 

[Flying Fox]

@ JB747

Thinking back to the QF30 emergency was it a case of 'Some are so dire that you'll be happy to just get the aircraft down, and don't care if it never flies again.' ?

What were your considerations when selecting a diversion airport?

 

[jb747]

JB, when you're made aware that someone from this board is on one of your flights, what do you do? (Or try to do?) Do you head down to say hi?

Depends upon the time of day, and the sector.

If I can, I'll go back and say hello. If not I'll have the cabin crew invite them up to the coughpit after landing.

 

[jb747]

Thinking back to the QF30 emergency was it a case of 'Some are so dire that you'll be happy to just get the aircraft down, and don't care if it never flies again.' ?

What were your considerations when selecting a diversion airport?

Initially, there wasn't too much selection being done. I just laid the heading bug across Manila on the map whilst we were in the descent. I knew the weather there was acceptable, and it was loaded into the FMCs as one of our diversion fields (we keep something loaded in the fix pages as the flight progresses, so there's always something in mind).

Once we had things sorted out, we looked at the alternatives. Clark was closer, but would require an instrument approach, which I didn't want to do with the degraded systems. Hong Kong was a bit further away, but offered a longer runway. We didn't want to be airborne any longer than we had to be...so Manila it was.

 

[Quickstatus]

Even a fairly complex diversion in India/Yangon worked pretty well.

What were the circumstances here?

 

[jb747]

What were the circumstances here?

Basically medical, but some complications that aren't for the 'net.

 

[Captain Halliday]

Re the MH diversion to ASP, I can confirm from an airport source who spoke directly to the PIC that DRW was their first choice and was discounted due to weather.

 

[jb747]

Re the MH diversion to ASP, I can confirm from an airport source who spoke directly to the PIC that DRW was their first choice and was discounted due to weather.

That's good to hear, but not unexpected. I generally don't have any issues with MAS.

I should have said earlier on, that I have no problems with this decision, quite unlike Air Asia when they diverted away from Learmonth.