Ask The Pilot

[jb747]

While understanding that V1, rotate, and V2 speeds are calibrated for the conditions, actual weight, etc, is there any benefit in delaying the rotation to reduce likelihood of tail strike - given in most cases, even heavily laden, there still seems to be plenty of runway remaining after the takeoff point?

It was called ‘overspeed’, and was used in some cases in the 747. Now, the electronic manuals will vary the speeds to maximise any benefit, without you having to specifically choose to do so, or even having any indication that it’s been applied.

I expect that you‘re referring to excess runway as being the black bit that’s left between the end and your lift off point. But, the calculations are more about the abort/go cases. For a balanced field length, the point at which you come to a stop from a V1 abort is calculated to equal the point at which you’d reach 35’ in the go case. Excess runway is any distance beyond that point, so the actual amount of excess is dramatically less than is evident in a normal take off.

There is a performance advantage to be had, as you’re accelerating on the ground, without the induced drag of the airborne wing. The negative is the rolling drag from the undercarriage, which itself, amounts to thousands of pounds in a 747. As best I recall though, the increase in speed to Vr was less than 10 knots.

 

[Saab34]

Why do some pilots use Aerodynamic braking? I saw this last week while at a holding point. The A320 did it. I asked another pilot recently who claimed its a pointless exercise, and growls at FOs who even attempt it. I assume if you are nose high and the speed all of a sudden goes plonk then potential damage to nose gear?

You see it at airshows quite a bit, JB is it a military procedure in landing?

 

[Aus ATC]

I expect that you‘re referring to excess runway as being the black bit that’s left between the end and your lift off point. But, the calculations are more about the abort/go cases. For a balanced field length, the point at which you come to a stop from a V1 abort is calculated to equal the point at which you’d reach 35’ in the go case. Excess runway is any distance beyond that point, so the actual amount of excess is dramatically less than is evident in a normal take off.

Thanks - my comment regarding excess RWY was also based on the fact that most of the time aircraft are well airborne (certainly over 35ft AGL at the departure end of the RWY). By implication then, V1 (abort speed) could be nominally greater than Vr or V2 (particularly for longer runways/lighter weight), but logic also suggests that once the rotation is commenced, V1 becomes moot.

There is a performance advantage to be had, as you’re accelerating on the ground, without the induced drag of the airborne wing. The negative is the rolling drag from the undercarriage, which itself, amounts to thousands of pounds in a 747.

No doubt the engineers could model the respective drag components to determine a "least total drag" scenario - theoretically at least given the short time frame of the rotation.

 

[jb747]

Thanks - my comment regarding excess RWY was also based on the fact that most of the time aircraft are well airborne (certainly over 35ft AGL at the departure end of the RWY). By implication then, V1 (abort speed) could be nominally greater than Vr or V2 (particularly for longer runways/lighter weight), but logic also suggests that once the rotation is commenced, V1 becomes moot.

Remember, it's 35' with one engine out. I'm sure you don't see that too often.

The actual requirement is 35', plus 1% gross gradient. But a tolerance of 1% is also allowed, leaving you with a minimum of 35'.

V1 (at light weights) often equals Vr, but it's never faster than it. Whilst in theory, you might in some cases be able to abort after becoming airborne, the reality of converting the climb out to a landing means that it would invariably be converted into a crash.

All you never wanted to know about climb segments:

Engine Failure During Takeoff - Multi-Engine Transport Category Jet Aircraft | SKYbrary Aviation Safety

The risk of engine failure during take off for transport category jet aircraft is mitigated by certification requirements and appropriate procedures to be followed by the flight crew.

www.skybrary.aero

 

[jb747]

Why do some pilots use Aerodynamic braking? I saw this last week while at a holding point. The A320 did it. I asked another pilot recently who claimed its a pointless exercise, and growls at FOs who even attempt it. I assume if you are nose high and the speed all of a sudden goes plonk then potential damage to nose gear?

Do not increase the pitch attitude after touchdown; this could lead to a tailstrike.
Do not attempt to hold the nose wheels off the runway.

Two lines from the 747 flight crew training manual.

You lose the effect of the nose gear/ rudder interconnect, which you may need for directional control. It creates lift, and so unloads the wheels, and it reduces the flow over the spoilers. The real heroes would also hold it way too long, and end up running out of back stick, at which point the nose would forcefully lower itself. Very poor technique.

It is pointless, and I also instructed my FOs not to do it.

You see it at airshows quite a bit, JB is it a military procedure in landing?

What you see at airshows doesn't necessarily align with the way things are operated day to day.

It may be a procedure in some aircraft, but not in anything I've flown. I recall one A-4 pilot who used to indulge in it. He wasn't anywhere near as good as he thought, and found himself on the wrong side of the CO, who objected to the rear of the drop tanks being dragged along the runway.

 

[flyer89]

Do not increase the pitch attitude after touchdown; this could lead to a tailstrike.
Do not attempt to hold the nose wheels off the runway.

Two lines from the 747 flight crew training manual.

You lose the effect of the nose gear/ rudder interconnect, which you may need for directional control. It creates lift, and so unloads the wheels, and it reduces the flow over the spoilers. The real heroes would also hold it way too long, and end up running out of back stick, at which point the nose would forcefully lower itself. Very poor technique.

It is pointless, and I also instructed my FOs not to do it.

Might be seeing things but United aircraft seem to do this constantly. Particularly back when they still flew the 747. YouTube videos seem to back that up. They land it like the shuttle.

 

[jb747]

Might be seeing things but United aircraft seem to do this constantly. Particularly back when they still flew the 747. YouTube videos seem to back that up. They land it like the shuttle.

I’ve looked through a bit of YouTube stuff, but honestly I haven’t found many instances of them going for much aerodynamic braking. A few of course, but mostly they’re just lowering the nose to the ground over 5-8 seconds, which is really just an example of smoothly flying it to the ground. That’s especially evident in A330 clips, where the pilots have to manage three touch downs....aft gear, forward gear, and nose.

Even the space shuttle doesn’t aero brake for any time. In its case, the main wheels are well aft, and the elevators will run out of authority quite quickly. As their nose is so high at touchdown (a delta wing characteristic), they need to fly it down before authority is lost. You can find a few examples of the nose thumping down, but mostly they just seem to be smoothly lowered over a few seconds.

I found one especially interesting clip, that showed a KLM 777 indulging in very lengthy aero brake. I’ll give him that it was well controlled and the nose came down smoothly, but it was also evident that the spoilers had not completed their extension, presumably because of there was limited weight on the wheels, and also because the landing gear trucks hadn’t completely un-tilted. So, basically he was defeating some of the aircraft‘s built in measures. I wonder if the auto brake was also inactive.

 

[RSD]

JB747 - I recallreading somewhere that Qantas flight crew had the option of filling in a form that said "I don't want to ever fly with person xx_ again" or something like that - presumably after a crew dynamics or personal conflict issue in the coughpit - did that ever get used much to your knowledge?

 

[jb747]

JB747 - I recallreading somewhere that Qantas flight crew had the option of filling in a form that said "I don't want to ever fly with person xx_ again" or something like that - presumably after a crew dynamics or personal conflict issue in the coughpit - did that ever get used much to your knowledge?

I don't know of any such form, so I don't know how many filled it in on me.

 

[Saab34]

AV, why isn’t single engine taxi used in Oz? Is it a CASA ruling? Very common in the US, even just taxing back to a gate with no delay they turn one off. Sydney taxi is comparable to many US airports in peak hour. Especially the trek down to 34R at 6pm

We sat in Sydney the other week for about 15 minutes for a gate. Seems like a lot of fuel could be saved in this space.

JB. Even for JFK. We on the QF 787 started both prior to the long hour taxi to the runway. The previous few takeoffs during my time there was A321 JetBlue and they didn’t start number 2 until we were about 5 for takeoff.

I asked a JetBlue Captain about engine start issues or engineering issues with this practice, and he said he has never heard of any issues and the company has been doing it since day dot.

 

[AviatorInsight]

AV, why isn’t single engine taxi used in Oz? Is it a CASA ruling? Very common in the US, even just taxing back to a gate with no delay they turn one off. Sydney taxi is comparable to many US airports in peak hour. Especially the trek down to 34R at 6pm

We sat in Sydney the other week for about 15 minutes for a gate. Seems like a lot of fuel could be saved in this space.

It is used in Oz. Virgin and Qlink both use it. I haven’t seen QF mainline, JQ, or Rex with a single engine taxi.

To be honest, you’re not likely to save too much fuel doing this. Some guys swear by it and others don’t. Personally, I don’t think delays are that bad where you need to shut one down for a taxi to 34R. Longest would be around 30-45mins and only use 150-200kg of fuel (we allow 200kg for the taxi on a normal day and up it to about 300kg if we see it’ll be a problem) and if you’re that tight on fuel to try and save around 100kg then perhaps you should’ve uplifted more. I can understand in the US however when you’ve got extensive delays where this would definitely benefit but Australia just doesn’t have that kind of a traffic problem.

On the other hand though, shutting one down after landing also may not really save too much fuel. The thing being here is, that once you’ve stopped you’ll need a lot of thrust to get going and keep that thrust up to gain the momentum to keep rolling. From my observation the benefits are negligible. So unless you come off 16L and were guaranteed to not stop, then sure you might save some fuel.

Of course this all based on a 737, and when you start talking in the tonnes of fuel for taxi (777 and the like), then it could be more beneficial.

 

[Saab34]

AV and JB. When was the last time you flew a single engine machine (172 etc..) for leisure? Is there any parts of Oz you would love to go and do a cross country Nav?

 

[jb747]

AV, why isn’t single engine taxi used in Oz? Is it a CASA ruling? Very common in the US, even just taxing back to a gate with no delay they turn one off. Sydney taxi is comparable to many US airports in peak hour. Especially the trek down to 34R at 6pm

We sat in Sydney the other week for about 15 minutes for a gate. Seems like a lot of fuel could be saved in this space.

JB. Even for JFK. We on the QF 787 started both prior to the long hour taxi to the runway. The previous few takeoffs during my time there was A321 JetBlue and they didn’t start number 2 until we were about 5 for takeoff.

I asked a JetBlue Captain about engine start issues or engineering issues with this practice, and he said he has never heard of any issues and the company has been doing it since day dot.

There is no CASA issue with single engine taxi (or even dual engine on the quads), and it is used after landing by QF.

As in all things aviation though, it comes with a number of buts. It was being pushed for use on the 380, but only had about 25% takeup by the Captains. Any saving is minimal, to non existent. Invariably, the power setting required on two will be greater than on four...and the total fuel flows end up being quite similar. If you have to stop (as you almost always do), the thrust required to get moving again is substantially higher, with much more of a jet blast issue. So, minimal fuel burn difference, and more jet blast.

All engines have cool down times after landing. It was 3 minutes on the 767 and 747, and 5 minutes on the 380. You can't shut down in that window, and as often as not you'll be at the gate in that time frame

Going the other way it can throw up issues. It puts another procedure that should be watched closely into the taxi. Attention will move away from one or the other, so there's a potential gotcha there. The biggest potential issue of all though, is the risk of a tail pipe fire on start. The ground engineers are watching for that, but there's no electronic means of checking. So, if the engine decides to catch fire in that way, you may not know until it becomes quite embarassing.

 

[jb747]

AV and JB. When was the last time you flew a single engine machine (172 etc..) for leisure? Is there any parts of Oz you would love to go and do a cross country Nav?

The last single engine aircraft that I flew was an RAAF CT4 in 1985. The lightest thing I've flown in the last 35 years was a 767.

I haven't bothered renewing my licence, so I expect that it has totally expired by now. I have zero interest in Cessnas or their ilk. One facet of retirement that I was looking forward to, was never having to have any interaction with CASA.

 

[Citoyen]

OK so today waited on board whilst QF 412 changed a tyre prior to takeoff ! Pleased we did not have to deplane, but kinda interested in difference between passengers on and off for all kinds of maintenance - is there an easy decision rule?

 

[AviatorInsight]

AV and JB. When was the last time you flew a single engine machine (172 etc..) for leisure? Is there any parts of Oz you would love to go and do a cross country Nav?

I circumnavigated the country twice. Once to gain my hours for CPL and thought it’d be a better idea than just doing the same. Bankstown - Bathurst - Goulburn - Bankstown nav 1000 times.

The second I did it as an instructor and went with the CPL students so I could knock out some of their dual for their flight test.

Last time I was in a lighty would’ve been about 10 years ago, and that was in a Pitts to just give my aeros a go. I then realised how expensive it actually is these days and would need another loan to get current again! So I haven’t been back since.

 

[RSD]

One facet of retirement that I was looking forward to, was never having to have any interaction with CASA.

Are they that big of a pain on the commercial side of the airport? I would have thought that the company would have been their contact point for most things apart from licences?

 

[jb747]

Are they that big of a pain on the commercial side of the airport? I would have thought that the company would have been their contact point for most things apart from licences?

I see them as a bureaucratic bully. In many ways weak, captured by the airlines they are supposed to regulate, but happy to use their weight against an individual. In particular, the medical side is somewhere between utterly incompetent, and criminally vindictive. Happy to mistakenly ground someone, but then making it an expensive, and very long winded, process to give back their medical. And never any admission of error.

 

[flyer89]

Last time I was in a lighty would’ve been about 10 years ago, and that was in a Pitts to just give my aeros a go. I then realised how expensive it actually is these days and would need another loan to get current again! So I haven’t been back since.

You should see how much it is now....

 

[flyer89]

Happy to mistakenly ground someone, but then making it an expensive, and very long winded, process to give back their medical. And never any admission of error.

I look forward to another few decades or so of dealing with them. Maybe they will be better in the future, but probably bigger and badder.