query regarding cruising altitude

Mailman

not a pilot so don't know but curious.

Is there a break even point for climbing to a certain cruising altitude for civil aviation?
Is it worthwhile climbing to normal cruising altitude if the trip is only say 250 miles in total.
I understand that it's less bumpy at higher altitudes which is a factor and there may be civil aviation authority regulations but can a pilot actually plan their altitude according to the length of trip they are taking or do they just go with what ATC give them?

highlydebased

Depends. There is level capping in place on certain IRL-UK routes.

Cap on SNN/CRK-STN area is FL310, MAN is 290. But with the fuel required for these trips and regardless of even a full load, it takes <60nm to reach cruise alt.

Must fly an odd level flying east/south and even levels west/north

The FMC gives an optimum level (best speed, fuel burn etc) which is generally used.

Mailman

but surely there must be some analogy similiar to striking a golf ball from a tee with a view to getting it to land on a green which would minimize energy(fuel) usage.
planes have natural glide ratios that would mean that on a short flight the engines would have to do precious little work from maybe two thirds of the way out to land on the runway.

highlydebased

Not really- Cruising at level 100 would use twice as much fuel as flight level 310 therefore climbing to 310 is most economic

PhoenixRising

Mailman wrote: »

but surely there must be some analogy similiar to striking a golf ball from a tee with a view to getting it to land on a green which would minimize energy(fuel) usage.
planes have natural glide ratios that would mean that on a short flight the engines would have to do precious little work from maybe two thirds of the way out to land on the runway.

There is, but on modern aircraft it's all calculated by the flight management computer on board the aircraft. It displays the optimum altitude to the pilots, based on aircraft weight, air temperature, wind and sector length. In general, to save fuel, you'd climb as high as you can and descend as late as you can using only idle power. In the real world, with ATC and level constraints that ideal scenario rarely arises.

Mailman

OK, brings me on to my next question which is do ATC have a role to play in minimsing fuel usage or do they not give a damn.
If more sophisticated ATC procedures are implemented could fuel usage on short hops be reduced across the board.
I'm thinking of busy airspaces like western europe where the distances from major city to major city are relatively short.

IRLConor

SAS have been doing some work in this area: http://www.aviationrecord.com/search-results.aspx?articleType=ArticleView&articleId=340

Mailman

That's what I'm talking about.

Since most flights are scheduled months ahead there is the potential for almost every flight to have a green landing.
Aside from the savings in fuel it seems the entire aircraft would be less stressed and it would result in a longer operational service life.

IRLConor

Mailman wrote: »

That's what I'm talking about.

Since most flights are scheduled months ahead there is the potential for almost every flight to have a green landing.
Aside from the savings in fuel it seems the entire aircraft would be less stressed and it would result in a longer operational service life.

Well, if everything went to plan that would be doable.

Accounting for pre-flight delays (missing passengers, missing baggage, security scares, last-minute maintenance) and weather (routing around it, missed approaches) would make it a lot more complicated.

Hopefully they'll figure out a way of expanding this technique to cover more and more flights. The green issues aside, it guarantees a specific landing time and reduces noise for landings. Both of those are useful goals themselves.

pclancy

At the end of the day each airline wants each flight to cost the airline as little as possible on fuel with an acceptable margin for safety so by using the planes FMC as described above, they're always going to be aiming for the most economic fuel burn. I was on a 40 minute flight a few weeks ago and they still managed to cruise at 24,000, truth is jet aircraft make it well worthwhile to climb quickly to an economic cruising altitude, even if it seems a bit high considering the distance of the flight.

They'll of course say its also through wanting to save the environment but in reality especially with low cost carriers its all about saving money and increasing profit.