Ask The Pilot

[jb747]

On the question of weights , other than loss of weight due to fuel burn does an aircraft lose any other weight during a long haul flight eg LAX - MEL ?

There are a couple of drain masts that dump some water, and some oil is burnt, but in the grand scheme of things nothing of consequence.

 

[lastrow]

no Loo contents? was this ever done?

 

[jb747]

no Loo contents? was this ever done?

Was it ever done...I expect many a bomber in WWII delivered personal payloads.

It's obviously stored. They use the empty chemtrail tanks.

 

[TheRealTMA]

Was it ever done...I expect many a bomber in WWII delivered personal payloads.

It's obviously stored. They use the empty chemtrail tanks.

I believe the Sunderlands of 461 squadron my dad flew in in '42 had a small flush toilet. Not sure where the flush went but most likely like a boat toilet.

 

[FrustratedQP]

. They use the empty chemtrail tanks.

Now you are just being cheeky.

 

[defurax]

I've been looking at HKG arrivals on FR24 today and I'd say almost 75% of the flights had to go around at least once, some twice and usually after two go around they go somewhere else. My question is are two go around some sort of red line which makes you decide to go somewhere else, or as long as you have fuel you might try as many landing as you can. I guess it must be kind of stressful to abort landing twice, especially after a long flight...not sure I'd like to be a pilot in bad weather! :shock:

 

[jb747]

I've been looking at HKG arrivals on FR24 today and I'd say almost 75% of the flights had to go around at least once, some twice and usually after two go around they go somewhere else. My question is are two go around some sort of red line which makes you decide to go somewhere else, or as long as you have fuel you might try as many landing as you can.

Many, perhaps most, companies probably have some form of guidance with regard to this. In our case, whilst it isn't a hard and fast ruling, they suggest that if you haven't gotten in after two attempts, then it might be a good idea to go elsewhere. Over the years I haven't gone around all that often, but HK is the only place where it's taken me three attempts to get a landing. On that day, the go arounds were both forced by different factors, and whilst it was windy, windshear was not an issue. Thinking about it, if you're having go arounds due to shear, then one attempt may well be enough (I bugged out of London after one go back in 2008). If the issue is not being visual at the bottom of the approach, then that may well change on the next approach...it isn't inherently dangerous, so a couple of attempts can be justified. As always, fuel gives options.

I guess it must be kind of stressful to abort landing twice, especially after a long flight...not sure I'd like to be a pilot in bad weather! :shock:

Which is a very good reason why you should have decent crew rest installations, and actually treat fatigue as the killer that it is. I expect that a huge percentage of landing accidents over the years have had a basis in fatigue....but it's always been easier for regulators and airlines to blame 'pilot error'. The 737 accident at Rostov, and the subsequent white wash, is a great example. I won't be surprised if it played a part in the AC event at SFO recently.

 

[Ansett]

expect that a huge percentage of landing accidents over the years have had a basis in fatigue....

This is what really worries with the proposed ULH flights such as MEL-LHR non stop. How realistic is it that a crew could get sufficient rest to prevent fatigue given that they are still with in the same environ during the rest period(s)?

 

[moa999]

So with today's announcement, are you jb747 happy about the swap of DXB/LHR for SIN.

Or does the slip not make much difference. Just another airport, another crew hotel?

Presumably means much shorter flying patterns.
Edit. I see from other threads that you could possibly do QF 35/1/2/36 so no change, though with only 1/2 380s continuing at least half the pilots will have to return

 

[jb747]

So with today's announcement, are you jb747 happy about the swap of DXB/LHR for SIN.

All of us like Singapore, and nobody will lament the loss of Dubai.

Or does the slip not make much difference. Just another airport, another crew hotel?

The hotel in Dubai was particularly nice...so nice that there was no need to ever leave it.

Presumably means much shorter flying patterns.

I have no idea how they will build the patterns. One issue with the 380 for quite a while has been the lack of short patterns to help even up the lines of flying, and also for items like route checks or training. They may build patterns to London for both Sydney and Melbourne based crews...that would make sense, but we won't know until the patterns are built.

Personally, I hope the Melbourne crews get some Londons.

 

[ChrisGibbs]

Was on this mornings 1/9/17 QF412 A330-200 MEL-SYD service. During the pre-pushback PA from the Captain he said the FO would be flying the sector. The approach onto RWY16R into SYD was normal with a nice view of a QF737 making a parallel but higher approach than us onto 16L. Based on the windsock there looked to be a slight SW breeze. The landing was nice and smooth with what appeared to be minimal reverse thrust and braking. As we passed through the intersection of RWY25/07 there was significant increase in the amount of braking combined with louder reverse thrust. We exited off RWY16R using one of the high speed run off taxiways B8. A couple of questions:


- Do the ground controllers direct you to or assume that you will use a specific taxiway as you depart a runway?

- Would the PIC override the PF by the application of additional reverse thrust and/or braking to expedite the departure off a RWY?

- Can the situation arise where the brakes overheat on landing and lead to a subsequent delay in the turn around of the aircraft for its next sector?

- What is the maximum ground speed that you can exit off onto a taxiway? Understanding this will vary dependant on the A/C involved. In the case of the A330 and in this particular case if we overshot B8 I would anticipate we would have been on the active runway for another 20+ seconds before we could exit off at B10 making the sequencing on departures and arrivals a lot harder...

Thanks in advance...

 

[andmiz]

It's been a while since I've answered one so here's a crack.

- Do the ground controllers direct you to or assume that you will use a specific taxiway as you depart a runway?

They may; however it's only a suggestion/request as they're not the one trying to make the action happen. We do try to minimise runway occupancy however, and helping them out generally helps us out too, as the ground controllers will have a plan on what taxi route they want you to use, and straying away from that may mean taxi delays.

- Would the PIC override the PF by the application of additional reverse thrust and/or braking to expedite the departure off a RWY?

Likely they'd make a suggestion to increase the deceleration efforts, rather than actually take over control of the roll-out and do it theirselves. If any flight control deflections are being made throughout the roll-out due to crosswind, these could be lost while the transfer of control takes place, leading to a decrease in aircraft control.
In your scenario in SYD on 01SEP, it could have simply been the FO deciding early in the rollout to pull it up a bit quicker than planned for whatever reason; many reasons for this.

- Can the situation arise where the brakes overheat on landing and lead to a subsequent delay in the turn around of the aircraft for its next sector?

Absolutely. Hot brakes are an issue, especially on the A330. Some Airbus' will have brake fans installed which help to increase the airflow around the brakes and dissipate heat. Ground crews may have fans they can install around the wheels to dissipate the heat also.
Rejected takeoff performance data is predicated on certain brake wear and temperature limits, and if the brakes are too hot prior to takeoff, the performance data is invalidated. All airliners have minimum brake temperature turn-around charts, or a minimum brake temperature requirement prior to takeoff. If the brakes are applied improperly during the taxi-out for takeoff (such as riding the brakes), the temperature may also be too high. On the A330, 300 degrees C is the limit before takeoff.

- What is the maximum ground speed that you can exit off onto a taxiway? Understanding this will vary dependant on the A/C involved. In the case of the A330 and in this particular case if we overshot B8 I would anticipate we would have been on the active runway for another 20+ seconds before we could exit off at B10 making the sequencing on departures and arrivals a lot harder...

Absolutely correct. Again touching on runway occupancy, the approach spacing is progressively decreasing through the industry to meet passenger demand, so accurately making your desired taxiway is important. On types such as the A380 or A350, they have a BTV (Brake To Vacate) system, where you select which taxiway you wish to vacate at, and it will modulate the autobrake application to meet your set requirements. It'll aim on getting you at 10kt, 65 meters before your desired exit.

On the A330 (and generally on other types too) 10kt for a 90 degree turn, and 50kt for the rapid exits.

 

[jb747]

Was on this mornings 1/9/17 QF412 A330-200 MEL-SYD service. During the pre-pushback PA from the Captain he said the FO would be flying the sector. The approach onto RWY16R into SYD was normal with a nice view of a QF737 making a parallel but higher approach than us onto 16L. Based on the windsock there looked to be a slight SW breeze. The landing was nice and smooth with what appeared to be minimal reverse thrust and braking. As we passed through the intersection of RWY25/07 there was significant increase in the amount of braking combined with louder reverse thrust. We exited off RWY16R using one of the high speed run off taxiways B8. A couple of questions:

- Do the ground controllers direct you to or assume that you will use a specific taxiway as you depart a runway?

They may ask for a specific taxiway, though that isn't all that common in Oz. Happens on most landings in Dubai. There is no requirement that you actually give it to them though...

- Would the PIC override the PF by the application of additional reverse thrust and/or braking to expedite the departure off a RWY?

The captain can override the FO any time he feels like it. In reality though, if you want an earlier taxiway, it's easier to just tell him. A common braking technique is to release the autobrake immediately after touchdown, and then to do no braking at all until about 100 knots. Then apply quite heavy braking in one go, back to about 20 knots. It results in cooler brakes overall, compared to light to moderate braking from touchdown.

- Can the situation arise where the brakes overheat on landing and lead to a subsequent delay in the turn around of the aircraft for its next sector?

Most certainly. It is a very real issue on the 380, with 90 minute turnarounds. In Dubai, it's hot, you often land slightly downwind, and you always need K8 or K9. The brakes there are always cooled by the ground engineers with conditioned air. They often hit 500ºC, and sometimes appreciably more. In Melbourne they don't have any means of cooling the brakes, so if you heat them too much, it will delay the next departure. We will consider what the aircraft is doing next when deciding on how much braking, whether to do it manually or automatically, how much reverse, and which taxiway.

- What is the maximum ground speed that you can exit off onto a taxiway? Understanding this will vary dependant on the A/C involved. In the case of the A330 and in this particular case if we overshot B8 I would anticipate we would have been on the active runway for another 20+ seconds before we could exit off at B10 making the sequencing on departures and arrivals a lot harder...

B8 is 90º entry, so you need to slow to about 15 knots before you can turn in. You can enter B7 at higher speed...but it ends in a sudden turn and grass, so I'd not be too enthusiastic. In theory you can enter a high speed at up to 50 knots, BUT, a real HS taxiway has entry and exit angles that are the same, whereas many in Oz end in nasty decreasing radius turns (Sydney A4), so you really can't be any faster in them than a 90º exit. If you miss the taxiway, then it's an SEP (ref Douglas Adams).

 

[serfty]

Today I have running 50 minutes late today MEL-BNE.

This is due to the inbound from LST arrivian at the gate 95 minutes late (VA1365).

Looking at Expertflyer, I see the following comments:

LST                    1050A D    3   
MEL              1150A
3LST/ETD1215  *2048
4LST/OUT1218 OFF1223 DL93/41/0031/0057 CAPTAIN TO VA1295 ^6 MIN CX FO PREP ☨ BOARD*2123
2MEL/ETA1315  *2152

Does that mean the original captain was subbed?

 

[petercr]

If you miss the taxiway, then it's an SEP (ref Douglas Adams).

Just a pity the A380 isn't equipped with Bistromathics (another Douglas Adams ref)... would make flying a whole lot quicker

 

[jb747]

Today I have running 50 minutes late today MEL-BNE.

This is due to the inbound from LST arrivian at the gate 95 minutes late (VA1365).

Does that mean the original captain was subbed?

VA1295 operates from Melbourne to Cairns....so I'd read it as the captain going from your flight to the Cairns flight on arrival in Melbourne.

 

[serfty]

Thanks - Cairns flight is boarding late so likely waiting for them. Ironically I'm going to Cairns but via BNE my original 100 minute connection to has been halved.

[Update]Not that I should worry too much as my inbound and outbound at BNE are both showing the same gate there. [/update]

 

[Captain Halliday]

A few pages back I recall jb saying that not much time can be made up on most flights - even long sectors - without substantial wind assistance. Approx. 15mins on LAX-MEL IIRC.

Does altitude make a difference to how much you can make up or does changing altitude just get you better winds?

On shorter sectors where MTOW and endurance aren't a big factor does taking extra fuel but flying a lower altitude allow you to go quicker?

The background to the question is that last night's QF846 SYD-DRW was 44 mins late off the blocks. Along with the usual PA the Captain said he'd "added extra, we'll drop down a little lower where we can go faster and try to make up some of that time". FWIW arrival was only 10 mins late.

 

[jb747]

A few pages back I recall jb saying that not much time can be made up on most flights - even long sectors - without substantial wind assistance. Approx. 15mins on LAX-MEL IIRC.

Remember that wind assistance isn't just a case of picking up extra ground speed from the wind. Changing altitude to get out of adverse winds is just as important.

Does altitude make a difference to how much you can make up or does changing altitude just get you better winds?

You need to start by having a think about the way aircraft speeds are chosen. Basically, at lower levels, we fly a 'best' IAS. That IAS results in a TAS that varies with altitude. IAS and TAS are equal at sea level, but TAS is approximately double IAS at FL400. So, for a given IAS, the higher we go, the better the TAS.

But, mach number provides an upper limit to the IAS, and as we climb we'll eventually hit a point at which our constant IAS reaches our target (or limit) mach number. In most cases this happens around FL300. So, IAS below that level and then mach number above. Now though, as we climb and hold that constant mach number, the IAS starts to reduce. The upshot is that you'll normally hit your maximum TAS at the IAS/mach crossover.

So, if there were no wind, we'd have the maximum groundspeed at the point of maximum TAS. But of course, there is wind. The wind change can be quite linear as you climb, whilst at other times there are large changes over quite short level changes. That means that the altitude for maximum groundspeed could vary dramatically, and it will vary with the direction you're travelling.

On shorter sectors where MTOW and endurance aren't a big factor does taking extra fuel but flying a lower altitude allow you to go quicker?

The difference in aircraft speed will be marginal at best. For instance in the 380 we normally cruise at around mach .84. But mach .87 is as fast as you can reasonably go, and even then you'll run the risk of hitting the Vmax every now and then. That's a difference of about 18 knots of TAS, which over the course of a short sector amounts to only a couple of minutes.

If you look at Melbourne-Sydney sectors, in the 767 days it was common for the south bound aircraft to be at about FL280, whilst those going north were up around FL370. Basically, on those flights the south bound flights were being operated down low to get out of the wind, whilst those going north were maximising it. They were probably both operating at about the same mach number.

The background to the question is that last night's QF846 SYD-DRW was 44 mins late off the blocks. Along with the usual PA the Captain said he'd "added extra, we'll drop down a little lower where we can go faster and try to make up some of that time". FWIW arrival was only 10 mins late.

The winds on that sector would have a strong headwind component. Going lower should get you less wind.

If we can get maximum TAS at around FL300, then why do we go higher? Well, the aircraft has a couple of competing things happening that affect our choice of altitude and speed. The wing has a best angle of attack, so ideally we'd like to fly at a speed that gives us that AoA. As our weight reduces, the speed for that AoA will also reduce (and recall that we do reduce cruise speeds as the flight goes on). At the same time, the engines have a speed at which they are most efficient...call it about 85% thrust. So, we want to chose an altitude that will give us that best IAS/AoA whilst simultaneously requiring the engines to be at that best power setting. Ignoring ATC aspects, that pretty much defines your initial cruising level. But, as the weight reduces and you slow to hold that best AoA, you're moving the engines away from their best setting. This leads us to the step climbs that you see on most longer flights...where we'll climb again once we reach the point that the weight has reduced enough for us to get that best speed/power combination at the next level up.

 

[jukebox333]

JB - it's pretty common for planes to "clean up" as soon as possible after they become airborne; how much difference does this make in real terms to how the aircraft handles for you in the coughpit? Does it differ from one type to another?