Ask The Pilot

[por930]

Ummm JB, looks like you have moved up the ladder a tad...
Qantas Captain Bryan Welch ends record run on the 747 | Australian Aviation

 

[jb747]

Ummm JB, looks like you have moved up the ladder a tad...
Qantas Captain Bryan Welch ends record run on the 747 | Australian Aviation

The 'cadets' have been around for a long time. I only flew with Bryan once, about 25 years ago, when he was a new 747 Captain, and I was a new FO. After that, we were generally on different fleets.

 

[jb747]

Fuel. Not much happens without it. And there’s a lot of myths and theories about how much airliners carry, and the options that might exist at any given time.


We never “fill ‘er up”. If we did that, then we couldn’t carry any passengers, so the operation might not run for very long.


We don’t have an alternate at the end of every flight. Alternate fuel always costs money to carry, and on longer flights it will displace cargo or passengers. An alternate may be carried if required by the forecast weather, though that requirement can, as often as not, be fulfilled by carriage of 30 or 60 minutes of holding fuel.


Extra fuel that is added to the flight is actually used up. A rule of thumb is that any extra is totally consumed in 24 hours, so on a 12 hour flight, only half of whatever you added will still be there at the end.


The companies all have fuel policies that are approved by their national regulator. In general, their effect is to produce a fuel loading that is the legal minimum, at every point and certain defined cases in the flight. So, for instance, a Melbourne to LA flight could be planned with an additional amount to cover the requirement for engine out, or depressurised flight, from the worst point on the route. Sometimes that’s adequate. Sometimes I add more.


At the end of the flight, an aircraft is ‘legal’ if it lands with, at the end of the landing roll, 30 minutes of fuel remaining to dry tanks. Legal, but not a really good place to be. Various other allowances exist. An amount (a tonne or so) will be set aside for the approach (from about 1,500 feet). ATC nominated holding fuel should have been carried…and may, or may not, have been used. The biggest variable is just that…variable fuel. It’s normally 10% of the fuel required, but not for the whole journey, just to go to the nearest place that you might land; so it’s a constantly changing figure. Preflight, it might be 5 tonnes or so, but by the end of the journey, it might be just a couple of hundred kilos. If a flight burns more fuel than planned, you hopefully get it out of the variable.


Everything else being equal, at the end of the flight, you’ll have that 30 minutes required at the end of the landing roll, and whatever is left of the variable fuel. Plus any holding fuel that you didn’t use.


So, what happens if there’s some interesting weather. Preflight, you carry whatever the weather forecast requires. If it is forecast to go below the alternate criteria (a nominated set of visibility and cloud base figures), then you either need an alternate, or holding fuel for the period it will be below the criteria. In flight, when you look ahead at the weather, you consider whether you’re simply trying to make the operation legal (the weather is just below the criteria, the airport handles it well, and you don’t expect any delays). In that case, the bare legal minimum might be enough. But, if it’s a place that really socks in, has extensive holding and long queues (i.e. Dubai), then the absolute minimum is the last thing you want. How much extra? That’s up to individual Captains. But, they will all have a minimum figure that they’ll accept for arrival on the day.


Considering Dubai. As I head towards the coast of Oman, I’ll have that arrival figure in mind. If I don’t have it at all, then there’s no point in flying past Muscat, and I’ll divert as soon as possible.


I know that I’ll have to hold at Dubai. So, do I have to keep about 20 tonnes up my sleeve to return to Muscat? Or, is there simply a holding requirement. If I have to keep the alternate available, then I’ll have to leave the holding pattern and divert as soon as the fuel reaches that diversion figure (or a bit before). If I stay in the pattern beyond that time, then I’m committing to either a closer diversion, or destination.


If you think that there will be a lot of diversions, you might be better off diverting early. Holding for an hour, then diverting might cost you 3 hours before you get back to your destination. Do you have that much time available (crew hours don’t matter in flight, but you can’t take off intending to break them). Diverting early (before flying past Muscat) might only cost you an hour. The same logic applies looking at the LA-MEL sector when considering your options regarding Sydney. It’s much quicker to divert to Sydney before flying past it, than it is to go half way to Melbourne before turning back…and it should give an overall earlier final arrival.


A figure that might be acceptable today, may be woefully inadequate tomorrow. You can’t just stick fuel on for mum and the kids, because, as often as not you’ll end up hitting a weight limit. It’s a bit of a black art.


I’m not sure how clear this is…but I’m sure you’ll let me know…..

 

[clazman]

Can I assume there are only 1 fuel company at each airport?

Do the airlines have any control over who provides fuel at the airports?

Can we assume that the price varies between airports?

 

[smeacs]

Thanks, That was helpful for understanding fuel.

The only part that i'm still a bit confused about is the fact that carrying extra fuel uses extra fuel. The theory/ idea makes sense ( extra fuel = extra weight which needs extra energy to fly therefore you use more fuel) but the practicalities still seem a bit bewildering.

But I cant even work out what question to ask so don't mind me

 

[opusman]

The only part that i'm still a bit confused about is the fact that carrying extra fuel uses extra fuel. The theory/ idea makes sense ( extra fuel = extra weight which needs extra energy to fly therefore you use more fuel) but the practicalities still seem a bit bewildering.

That's the main reason why getting into orbit is so difficult / expensive

 

[jb747]

Can I assume there are only 1 fuel company at each airport?

Good question, to which I've never taken any notice. I don't see any reason why there might not be more than one supplier, though it probably comes out of the same tanks.

Do the airlines have any control over who provides fuel at the airports?

They have contracts with their supplier(s) of choice.

Can we assume that the price varies between airports?

Just like your service station, but I expect the variation is more on a country basis, especially with regard to local taxes.

 

[harvyk]

30 minutes to dry tanks, is that 30 minutes of fuel on ground or in a holding pattern?

 

[por930]

30 minutes to dry tanks, is that 30 minutes of fuel on ground or in a holding pattern?

Extract from jb's excellent fuel loading/usage explanation...."Everything else being equal, at the end of the flight, you’ll have that 30 minutes required at the end of the landing roll, and whatever is left of the variable fuel. Plus any holding fuel that you didn’t use".

 

[russ]

Can I assume there are only 1 fuel company at each airport?

Sydney has AMPOL, BP, Caltex, Mobil and Shell.
See http://www.airservicesaustralia.com/aip/current/ersa/FAC_YSSY_20-Aug-2015.pdf

Can we assume that the price varies between airports?

Yes it does.
See People, Prices, Places - Our Prices - Shell Global
Of course large fuel users negotiate substantial discounts.

 

[jb747]

The only part that i'm still a bit confused about is the fact that carrying extra fuel uses extra fuel. The theory/ idea makes sense ( extra fuel = extra weight which needs extra energy to fly therefore you use more fuel) but the practicalities still seem a bit bewildering.

The aircraft will be heavier than it would otherwise be. More power required. More drag. Higher fuel flow. Greater burn. To have an extra 5 tonnes at the end of a 12 hour sector would require an additional load of about 7,500 kgs at the start of the trip.

 

[jb747]

30 minutes to dry tanks, is that 30 minutes of fuel on ground or in a holding pattern?

30 minutes at 1,500 feet. Not much, but that's the worldwide minimum.

 

[D747]

So JB, in terms of the number of minutes at 1,500 feet, what is the lowest number of minutes that any commercial flight you have ever been involved with has had please?

 

[jb747]

So JB, in terms of the number of minutes at 1,500 feet, what is the lowest number of minutes that any commercial flight you have ever been involved with has had please?

Probably about 45 or so. I've never given myself a scare (he says whilst touching wood).Mostly I'm a wimp, and aim for about 60+ minutes. Lowest ever would be in the military, where about 10 wasn't unusual.

 

[RAM]

Probably about 45 or so. I've never given myself a scare (he says whilst touching wood).Mostly I'm a wimp, and aim for about 60+ minutes. Lowest ever would be in the military, where about 10 wasn't unusual.

....and degree of sweat in flight suit approaching 10 minutes fuel?

 

[jb747]

....and degree of sweat in flight suit approaching 10 minutes fuel?

You become used to anything. We sometimes took off with less fuel than the civilian minimum landing reserves.

 

[straitman]

You become used to anything. We sometimes took off with less fuel than the civilian minimum landing reserves.

Departing RAAF Richmond one day for a flight to Canberra via Sydney Harbour I declared minimum fuel on start up.

I'll let you draw your own conclusions.

 

[harvyk]

Departing RAAF Richmond one day for a flight to Canberra via Sydney Harbour I declared minimum fuel on start up.

I'll let you draw your own conclusions.

I've heard that it's not uncommon for the military to be a bit more lax on safety than in the civilian side, but I would have thought that putting a bit of juice into something worth multi multi multi millions would have been relatively cheap compared to the risk if something went wrong. Is there a reason they don't like to take up much fuel?

 

[jb747]

I've heard that it's not uncommon for the military to be a bit more lax on safety than in the civilian side, but I would have thought that putting a bit of juice into something worth multi multi multi millions would have been relatively cheap compared to the risk if something went wrong. Is there a reason they don't like to take up much fuel?

They aren't lax with regard to safety at all, but their priorities are totally different. Worst case in many aircraft is that you abandon ship...something that simply isn't done in the airline world.

The transport type aircraft will operate with similar reserves to civil aircraft, but the fighter types (and I'm thinking of older aircraft like the A4, Mirage, etc), only carried whatever fuel was needed for the mission, simply because more fuel means more weight, and that in turn means less available G. There is no point in going on a dogfighting sortie with a 5 g limit due to fuel loading. Drop tanks add more weight and drag, and were again carried as needed. Added to that, the aircraft could be extremely thirsty...depending on just what you were doing, you could burn through the available fuel in as short as 35 minutes, and we didn't have after-burning (I have a vague memory of the Mirage being able to do it in about 15). Fuel management was simply part of the game. Needless to say though, that we never accepted ATC delays (nor, in fact, would the military controllers dream of assigning them).

 

[mjt57]

Speaking of fuel management, saw this article in the Oz, today...

Cookies must be enabled. | The Australian

If the blurb can be believed they look like scrutinising how pilots manage their in-flight ops in order to get better fuel economies.

Wonder how this will work...