Ask The Pilot

[Himeno]

Does QF always use the same gates at DXB? Every time I've been there, the flight has used A1 or A24.

 

[jb747]

Does QF always use the same gates at DXB? Every time I've been there, the flight has used A1 or A24.

For some obscure reason, the numbers that you see for the gate from inside the terminal, and I see from outside are different. I think A1 is also A5, and A24 is A6...or something like that.

We generally use those two, or positions nearby.

 

[jb747]

Sim time again. In fact, my sim timing had expired, so I needed to get this one done before I could go flying again.


The exercises have gone through a number of iterations over the years, with the focus varying as CASA and management reacted to various events. They’ve had periods in which they were mostly line oriented (i.e. like normal flights), and have at times spent a lot of time ticking boxes for CASA…doing normal procedures that are rarely seen in flight, and which were treated as sudden death in the sims (no training, just get it right). And, now we’ve migrated back to a system that’s all about training. You don’t have to fail an exercise before being able to have a couple of goes at something.


The FO for this exercise was only there to provide support so some of the sequences designed for him weren’t needed. That actually allowed more time for me, which is always nice.


No gentle warm up. First take off had an engine failure at rotate. Clean up and fly back for a 3 engine ILS approach to Melbourne 16. Autothrust also dropped out, but sim instructor said it wasn’t him!


We looked at a number of TCAS events. Most required manoeuvering, but in one case, the system demanded level, and had other aircraft simultaneously pass under and over. Threading the needle.


Windshear at take-off, with 30 knots of tail wind coming in just after lift off. Battle your way out of that, and then it swings onto the nose. Managed not to crash or overspeed anything.


Unreliable airspeed. We looked at this in a couple of different ways, but basically the FO loses his IAS just prior to rotate. Mine hangs in until rotate, and then it fails as well. The failure is actually of all three air data computers, so you can’t get the normal displays back. The ISIS (standby display) works throughout, but really all you need to do is rotate normally to the target attitude, and push the power to TOGA. The law will eventually revert to direct, but you’ll be in a stable situation heading away from the ground. The checklist will ultimately have you turning off all three ADRs. IAS display will never come back, but you’ll get what’s called the BUSS, which is effectively an angle of attack display.


A two engine approach was next up. Normally we do these in the worst case, two out on the same side. Not only does that make the aircraft very asymmetric, but you also lose one hydraulic system, and with that, the ability to retract the gear. You’re basically committed once you start the approach. But, with one out on each side, minimal asymmetry (we lost 1 and 3), and the major systems remain available. Even autoland still works (so I made use of it). Because the aircraft has very little rudder applied, there’s nowhere near as much drag. The approach is almost normal, and there’s plenty of go around capability.


CASA has a requirement that Captains demonstrate an approach without approach slope guidance. So, a manually flown visual approach with no ILS or VASIS/PAPI. Just like Fred does in his Cessna.


Last thing for the day was a depressurisation and emergency descent.

 

[SFSC]

How capable would TCAS be in a multiple conflict event? Is there a design limit to the number of aircraft it could separate? Has there ever been a TCAS event involving more than two aircraft?

 

[jb747]

How capable would TCAS be in a multiple conflict event? Is there a design limit to the number of aircraft it could separate? Has there ever been a TCAS event involving more than two aircraft?

I'm sure there's a design limit, but I don't know what it is. The system is often displaying many aircraft, and it will be working solutions for all of them, so realistically, it can handle as many aircraft as I'm likely to see. There are issues, but they'll exist in any system.

In most aircraft the pilots have to manually fly the TCAS instructions. Since the advent of the system, this has really been the biggest failing. If you don't do exactly what it says, you'll make the situation worse. There are very limited cases in which your aircraft may not have the performance necessary (i.e. a climb resolution at very high altitude), but even in this case you'll be better off trading the performance, missing the other aircraft, and fixing whatever you're left with later. Newer aircraft can fly the TCAS instructions with the autopilot.

The manoeuver will always be in the vertical only. Vertical resolution is much better than lateral, so the system is much more certain of the vertical elements of the situation. Airliners don't turn worth a damn, so turning isn't really an option anyway.

TCAS escapes should be quite gentle, and it's very likely they wouldn't even be noticed in the cabin. A reversal, in which the system needs an immediate change from one direction to the other (either to miss a second target, or in response to the other aircraft not following the commands) would be the exception.

At the end of the day though, TCAS is there as a last line of defence. It's to cover ATC (and others) mistakes.

 

[Quickstatus]

Can you give us a typical TCAS audio instruction and subsequent instruction if initial is not followed.

 

[jb747]

Can you give us a typical TCAS audio instruction and subsequent instruction if initial is not followed.

Lots of information here: https://en.wikipedia.org/wiki/Traffic_collision_avoidance_system

And the operating instructions for one system here: https://www.bendixking.com/HWL/media/Pilot-Guides/006-08499-0000_7.pdf

 

[jukebox333]

*snip*

Last thing for the day was a depressurisation and emergency descent.

Out of curiosity, JB - any mixed feelings when that was simmed? ...or is it a case of you being so focussed on managing the event for your training that your mind doesn't let you wander back to QF30?

 

[eric2011]

I'm sure there's a design limit, but I don't know what it is. The system is often displaying many aircraft, and it will be working solutions for all of them, so realistically, it can handle as many aircraft as I'm likely to see. There are issues, but they'll exist in any system.

In most aircraft the pilots have to manually fly the TCAS instructions. Since the advent of the system, this has really been the biggest failing. If you don't do exactly what it says, you'll make the situation worse. There are very limited cases in which your aircraft may not have the performance necessary (i.e. a climb resolution at very high altitude), but even in this case you'll be better off trading the performance, missing the other aircraft, and fixing whatever you're left with later. Newer aircraft can fly the TCAS instructions with the autopilot.

The manoeuver will always be in the vertical only. Vertical resolution is much better than lateral, so the system is much more certain of the vertical elements of the situation. Airliners don't turn worth a damn, so turning isn't really an option anyway.

TCAS escapes should be quite gentle, and it's very likely they wouldn't even be noticed in the cabin. A reversal, in which the system needs an immediate change from one direction to the other (either to miss a second target, or in response to the other aircraft not following the commands) would be the exception.

At the end of the day though, TCAS is there as a last line of defence. It's to cover ATC (and others) mistakes.

1. What is the operating range of TCAS.
and
2. if there is a range, in theory TCAS could instruct you to climb to avoid a head on incident with a aircraft traveling at a wrong flight level, and put you onto a collision course with another traveling say 10 or 20 miles (outside the range of TCAS) behind it and at its correct flight level

 

[AviatorInsight]

1. What is the operating range of TCAS.

TCAS works on a 3D airspace around the aircraft. The dimensions of this airspace depend on on the closure rate with conflicting traffic.

As JB noted above, an RA is a prediction that another aircraft will enter the TCAS conflict airspace within 20 - 30 seconds. A TA is is in the 25 - 45 second range, and proximate traffic is neither an RA or TA but is within 6nm and 1200ft vertically.

and
2. if there is a range, in theory TCAS could instruct you to climb to avoid a head on incident with a aircraft traveling at a wrong flight level, and put you onto a collision course with another traveling say 10 or 20 miles (outside the range of TCAS) behind it and at its correct flight level

Again, depends on closure rate, however once we are clear of conflict (and believe me it doesn't take long for this to occur) we return to the assigned flight level. Should there be other conflicting traffic, then TCAS will sort that out also. It is in constant communication with other aircraft.

 

[jb747]

1. What is the operating range of TCAS.
and
2. if there is a range, in theory TCAS could instruct you to climb to avoid a head on incident with a aircraft traveling at a wrong flight level, and put you onto a collision course with another traveling say 10 or 20 miles (outside the range of TCAS) behind it and at its correct flight level

TCAS displays and ranges vary dramatically with aircraft type. We regularly see others out at 80 miles or so, and yet at other times, can't see aircraft we know are only a few miles away. It isn't really meant for that sort of area surveillance, so it's more a bonus than a feature.

The system will not order any change until in very close proximity to the target. Head on you'll probably be inside 10 miles, so your scenario can't occur. With two close targets it will talk to them both, and arrange a combined outcome. Where an initial solution puts you into conflict with a second aircraft, it will eventually react to that. That's where you may end up with reversals. It works extremely well...as long as you follow it, and recognise that its solution may well take you through the other aircraft's height.

 

[jb747]

Out of curiosity, JB - any mixed feelings when that was simmed? ...or is it a case of you being so focussed on managing the event for your training that your mind doesn't let you wander back to QF30?

I don't think about QF30 in the sim exercises...though to be honest sometimes the sims aren't as well handled as we managed on that day. The sim exercises exist partially as a place to make your mistakes...and I manage that.

 

[Captain Halliday]

How frequently is TCAS triggered? Is there industry data on X activations per 100,000 flights for example?

 

[flychrisfly]

For some obscure reason, the numbers that you see for the gate from inside the terminal, and I see from outside are different. I think A1 is also A5, and A24 is A6...or something like that.

We generally use those two, or positions nearby.

Any reason why? Or do you just go where you're told?

 

[AviatorInsight]

How frequently is TCAS triggered? Is there industry data on X activations per 100,000 flights for example?

I haven't found any data on the amount of activations per flight.

As to how frequently it is triggered, I would love for it to be very low if none at all! Having said that, I have only had to have done a couple of RAs so far, plenty of TAs and proximate traffic though as one would expect in busier airspace.

 

[jb747]

How frequently is TCAS triggered? Is there industry data on X activations per 100,000 flights for example?

No idea...and I doubt that the information would be readily available. Resolution advisories are very rare (which is good). I've seen two, and both were associated with opposite direction runway operations. Earlier software was more prone to unnecessary (though not spurious) warnings.

 

[jb747]

Any reason why? Or do you just go where you're told?

Different needs for the internal versus external user. And probably different history for the naming convention.

We go where we're told. It not like parking at Coles, where you find an empty space that looks big enough...

 

[petercr]

It not like parking at Coles, where you find an empty space that looks big enough...

coins a new phrase - 'plane-park rage'... (especially at this time of year)

 

[JohnM]

coins a new phrase - 'plane-park rage'... (especially at this time of year)

Don't want any door dings....

 

[jb747]

Off topic...but I saw someone at my local supermarket the other day, who, after carefully assessing the size of the available space, drove straight into the adjacent car. And that's why I park at the far fringes of any car park. It would be nice if even 5% of the aviation standards were applied to drivers. Sadly, the driving standard is slowly being applied to flying.