Filed Altitude below 10,000ft (ATC related)

[Morgan Davies]

Besides turboprop aircraft, why would any other pilot, namely of jet engine aircraft want to file an altitude below 10,000 ft? Correct me if I am wrong, since I am not a real world pilot, but don't jet engines operate more efficiently at higher altitudes?
 

 

[Andreas Fuchs]

It all depends on the distance of the flight and maybe a more direct route can be taken when staying low. But, yes, normally you want to fly at or above10,000ft/FL100 to stay above uncontrolled VFR traffic.

[Tobias Dammers]

Only reasons I can think of would be a) training / test flights aimed at practicing things below 10,000 feet, and b) flights too short to climb beyond 10,000 ft, probably repositioning flights - for example, Transavia sometimes needs to ferry 737's between EHAM and EHRD, BAW ferries Embraers between EGSS and EGLC, stuff like that. And even when the flight is technically long enough to climb beyond 10,000 ft, airspace restrictions might still make this impossible - e.g., many SIDs from EGLC keep you below 10,000 ft until you reach the coast, so as not to disrupt other traffic in the area.

[William Teale]

7 hours ago, Morgan Davies said:

Besides turboprop aircraft, why would any other pilot, namely of jet engine aircraft want to file an altitude below 10,000 ft? Correct me if I am wrong, since I am not a real world pilot, but don't jet engines operate more efficiently at higher altitudes?

As outlined above, to save fuel, or to comply with airspace restrictions.

Jet aircraft burn a lot of fuel to climb, quite a bit less fuel in cruise, and less again in descent. For a very very long mission profile, the high fuel burn at the start of the mission is more than offset by the fuel saved in cruise by cruising at a more fuel efficient altitude. For short range missions, this no longer holds true, and it can be worth cruising less efficiently, in order to avoid burning excessive amounts of fuel in climb.

In the long distance case, we might burn an extra 1000 lbs of fuel in order to climb higher, because over 800 miles cruise, we will save 2500 lbs of fuel. Its worth spending the extra fuel in climb, to save fuel in cruise, because we will land with more fuel remaining.

A short distance case might be choosing not to burn the extra 1000 lbs fuel to climb higher, because over 80 miles cruise, we would only save 250 lbs of fuel. Because climbing in this case would cost more fuel than the fuel savings, it would be worth cruising lower to save fuel.

Depending on the aircraft, we might also be power limited. At max gross weight, its possible for an F-16 to reach about 22,000 ft at max power, but its going to take 90 miles to do it. For a short range flight, that might just not be worth it.

[Robert Shearman Jr]

Weather / turbulence / icing could play a role from time to time also, over shorter distances that is. 

[Nick Warren]

Tower Enroute Control (TEC) routes notably in Southern California have jets below 10,000 on many routes.  These are pretty short duration flights though.

[Sebastien Bartosz]

Same in NY area. Lots of routes below 10000 (JFK-PHL for example)