fixed reserve
 

Wondering if anybody has an idea what fuel rate the fixed reserve is based on? Is it based on cruise rate? Or is it a holding rate at 1500' above the runway? Or a holding rate at some higher altitude?

A reference to the answer would be appreciated.

Mango

Good Question
 

I bet this gets plenty of answers, how many are correct is another matter.

I believe it to be, not 100% sure but it should be your cruise rate, after all, unexpected head winds against your cruise speed and fuel burn is not the same as holding above a fogged in field, and if fog is expected you should have other plans.

If you eat into reserves holding, you will have more than an hour anyway.

For me and my PVT OPS, I work on 1 hr cruise rate.

Cheers
J:ok:

FFR is based on holding at 1500'

Don't much matter what the book says - you'd be pretty stupid to base it on anything other than cruise rate!

Ref: The Rat:cool:

15-20 years ago, the rules regarding fuel carriage were changed. Prior to the change, the requirements (e.g 45 minutes FR, 15% VR) were spelt out in AIP. Now, there is just one rule:

Thou shalt not run out of fuel - Reg 234, CAR 1988

What had been required fuel carriage prior to the rule change became recommended from then on. This was effected by transferring the various paragraphs out of the AIP and into an advisory document (CAAP 234-1).

So what does the CAAP document say about fixed reserve? In the definitions section, for "fixed fuel reserve", it says:

Following the rule change, commercial operators were required to spell out their fuel carriage requirements in their operations manual. This allowed the operators to devise fuel requirements that were appropriate for their operation. So, the definition of "fixed reserve", and whether it is even required, is up to the holder of the AOC (in the case of a commercial operator).

Of course, private operators are also free to devise their own requirements - the CAAP document only makes recommendations.

You can download the CAAP document from here:

http://www.casa.gov.au/download/CAAPs/ops/234_1.pdf

Rat, the holding fuel flow rate at 1500' may often be higher than the cruise fuel flow rate.

Damn, you are right - I forgot about those hair-dryer powered things. Otto and I have been pals for too long.

How about: "You'd be stupid not to use an appropriate rate for the aircraft type you are operating".

R:cool:

So I guess 90% of the operators around the country are stupid right?

Tip: Engage brain before mouth.

:rolleyes: :rolleyes: :rolleyes:

If in doubt, check the ops manual. I have seen them differ on this one.

Can you please elaborate on this? Are you saying that your fuel flow rate at max endurance IAS, 1500' is greater than at max range IAS? Is this a density altitude effect? i.e. you're assuming cruising at FL300+? Can you explain why this is? This seems to imply that if you throttle back, you go faster, which I'm sure is not actually the case.

For what types would this be the case?

A

APMR

Thanks for that, I think you have hit it on the head. I suppose, at the end of the day, company SOPs govern what the fixed reserve will be.

Mango

G'day Andy.

Sorry but I guess it depends how you read what I wrote. My fault - goes to show how hard it is to imply subtle nuance on the web. I'm talking about cruise flow flow rate at high altitude as compared with holding fuel flow rate at 1500'. Most jet aircraft (well, mine doesn't so I'm assuming the rest are the same) don't have cruise data for 1500' but comparing cruise data at max endurance cruise ie. holding fuel flows at say FL300+ as compared with holding fuel flows at 1500', the lower fuel flow will be achieved at the higher altitude.

Can't remember the aerodynamics and BGT to explain it but primarily jet engines are more efficient the higher you go.

Hope this helps clarify things.

Cheers.

Jet engines are more efficient up high because the air is less dense...for given N1 the EEC looks at how much air is going in the front and mixes it with the right amount of fuel.

Up high less air goes in the front so less fuel required for the same fuel/air ratio.

Less thrust produced but less required due air less dense so aeroplane has a higher EAS or Mach number.

Or something like that....been a VERY long time since I sat BGT:ok:

I heard someone say once that the fixed reserve is 45 minutes of an average fuel flow figure. Eg. get the climb fuel flow using pressure altitude and temp. which will be higher than your cruise, get the cruise fuel flow figure and then the descent figure, average the three to get an average fuel flow and take 45 mins at that rate. In general the climb and descent usually cancel each other out and the cruise rate is generally sufficient. In the bug smasher I am flying we use a block figure of 50lph which works and we take a fixed reserve of say 37-38. Depending on altitude and temp the figures when done properly can come out normally around 45 so that would change it by not much, and the 50 has a good buffer on that for unexpectancies like low altitude holding. But thats the way that I believe is the proper way. I dont know anyone that makes this fine adjustment every time they go flying, 50 seems quite reasonable to me. Someone correct me if what I overheard is a load of sh**. Cheers JB

Chimbu

FYI the holding fuel flow for a Trent 700 or 800 is in fact lowest at alt's between FL150-FL200.

.. and some of the older jet engines will give you more fuel flow sitting at the holding point with idle throttles ... than cruising at 330 or thereabouts .. low level is not nice for these sorts of machines ...

Messiah i wasn't trying for a type specific treatise on alt/FF....just a very basic broad brush on FF in jets across the spectrum of altitudes between circuit height and coffin corner:}

RELAX:ugh:

jt, sounds a bit like the Speys in the Fokker....on takeoff and innitial climb your FF suggested tanks dry about half way to desto...ahh crackle power:ok:

Was only saying it out of interest hence FYI. Maybe YOU need to relax.