Biz Jet Cruise Altitude

[Bjarnum]

Two questions for some University research:

1. What is an average Biz Jet Cruise altitude on ultra-long haul flights, say Transpacific or Transatlantic on AC types e.g. Falcon 7X, Gulfstream G550, Global X etc?

2. Are these cruise altitudes higher/lower then for ultra-long haul commercial flights on say a 747, 777, A340 etc?

Cheers

[chubbychopper]

The corporate types you mention all have service ceilings that exceed those of the airline types, so the corporate types will generally cruise at higher levels.

The actual cruise level that any type elects to fly will be determined by a combination of the aircraft weight, ambient conditions and economic considerations related to time and fuel consumption. On a long range flights a continuous climb as weight reduced would be convenient, until descent of course. Since this is not practical "step climbs" are made.

[ksjc]

We spend about 90% of our time at FL430 or FL450 in the GLEX. Certified to FL510 but I don't know anyone who goes that high.

[Trim Stab]

Even short-range bizjets (eg C525) cruise at FL410-FL450.

[RAFAT]

Exactly what chubbychopper said, and that's with a Citation XLS.

[FrankR]

In a 550, initially FL410 fully loaded , and we can go to 450 after 4-5 hours, and climb to 510 ten minutes after we request descent.

... (The last part was an attempt at humor)

.83 or .85 normally, and .80 for long haul over 12 hours



FR

[Pace]

Frank

Your 550 must be on Steroids compared to my 550 :E

Pace

[smallfry]

In the 550 I operate, we will always be in the 40's, looking for higher as soon as we can get the weights to optimum. Getting lighter at the end of flights we are often at FL470 and even FL 490 if we can. We can't legally go to FL 510 but even if we could, we would be on very little fuel.

[FrankR]

.... Where do you normally fly Pace?

[Pace]

Frank

It was a joke! My 550 is a C550 Lovely old Citation 2 and good for the soul :{

Pace

[Jet Jockey A4]

We operate a Challenger 604 a Global Express 5000 and a Global Express XRS.

As mentioned above (in previous posts) for operational reasons a modern ultra performing biz jet can usually operate at higher altitudes when compared to the airliners.

The Challenger 604 is limited to FL410. Usually on long flights we will cruise it between FL370 and FL410.

On the Globals even if it is certified to FL510, the highest I have flown it so far was FL470. This altitude was used on a short flight (about 3 hours in length) for weather avoidance or on very long range flights like Beijing to Montreal (non-stop in 12 hours 15 minutes at a long range cruise of M0.83).

However this said, for passenger comfort and pilot fatigue we usually fly the Global no higher than FL410 (unless operationally needed) because at that flight level we have a cabin pressure of only 3600 feet which makes a big difference to both passengers and crew.

FYI, the 604's cabin pressure at FL410 is around 8000 feet (4400 feet higher than the Global's cabin)!

[Bjarnum]

Excellent, thank you for your help. So there are obviously many factors in choosing a cruise altitude: weight, range, weather, passenger comfort and pilot fatigue etc.

As per commercial airliners on ultra-long haul routes, their cruising altitude would be typically FL36? thus lower then business jets on the same route.

[Denti]

Depending on load usually in the thirties when starting, later on up to FL430 shortly before top of descent. Of course all depending on type, route length, passenger and cargo load, winds etc. Keeping lower for passenger comfort due to lower cabin altitude is usually not a main topic in airline operation, it is mainly about optimum level flying.

[Jet Jockey A4]

Airlines are there to make money so optimized flights are the norm. I can't ever recall an airliner above FL410 (except the Concorde) and even FL410 is pushing it for most airliners.

Some business jets can fly higher because they are certified to higher altitudes but like you said, weight, weather, winds and fuel burn are all part of the equation to accomplish the mission.

Since airlines are looking at cost all the time it is normal for them to optimize their flight patterns (to cut cost and make revenue) where as corporate jets are usually owned by wealthy corporations or individuals that don't require their aircraft to bring in or make money for them. In that sense they can operate their aircrafts (if need be) at less than optimal efficiency and stay at lower altitudes for either comfort reasons like I mentioned before or to cruise at a higher Mach/True airspeed regardless of how much fuel is being burnt out the tail pipes.

[TopBunk]

I have taken a B747-400 up to FL430, just once, as it is very rare to have the circumstances condusive to enable it. Indeed, I don't recall going higher than FL400 or maybe FL410 ever before this one off.

It was coming back into LHR from JFK in 2009 on exiting the NAT system over Southern Ireland and they even coordinated a handover to London at that level rather than the usual FL330(?).

Anyway, I have the photo to prove it somewhere!

[421C]

Out of interest, what is the engineering reason bizjets are designed for typical optimum cruise in the mid 40s and airliners in the mid-high 30s?

The higher a jet goes the lower the specific fuel consumption? So higher is better. But, I guess the negatives for this are the airframe penalties for operating at a higher level (in terms of higher press. diff.) and relatively higher thrust engines to be able to achieve the climb. But then both these trade-offs seem to me to scale up and down across transport jets and bizjets? Is it that the bizjet operators prefer shorter runway capability, so the greater SL thrust has other benefits? Or is it wing related - something like a long slender wing optmised for very high levels is structurally too heavy if scaled up to airliner size? I don't know if there are certification issues with high levels that are more easily met in a smaller aircraft? I can't think what they might be, it feels like the smaller aircraft could depressurise much faster, so it's not "speed of pax accessing emergency oxygen" thing.

Sorry if this rambling question has misunderstood the technicalities!

[smallfry]

Straight line directs! :-)
Longest I have had so far was Cabo, Mexico, to oceanic entry point on the east coast of Canada.

[TheiC]

421C,

Good post. You'd enjoy this:

http://www.amazon.co.uk/The-Design-Aeroplane-Darrol-Stinton/dp/0632054018

[SFI145]

I think another important factor is that many biz-jets are operated as private flights where the pilot oxygen requirements are less stringent. Whereas for example under Part 135 one pilot must be wearing an oxygen mask at all times above FL350.
If one pilot leaves the flight deck above FL250 the other pilot must be using the mask.

http://www.faa.gov/pilots/safety/pilotsafetybrochures/media/Oxygen_Equipment.pdf

[Jet Jockey A4]

In Canada we have to wear the oxygen mask above FL410 too... Just another reason not to go above.

[GIVSP]

Another factor limiting max ceiling is the requirement to return to (I believe) 15,000ft within 4 minutes - so wing design, speed brakes, MMO/VMO are all factors that contribute towards how fast an aircraft can descend and therefore the maximum attainable rate of descent can be a limiting factor in setting the service ceiling. Thrust is not always a factor - I believe the GLEX, G550 and C-750 engines are all designed to operate up to FL600.

As previous posts have noted, even though these aircraft all have FL510 as a ceiling, completions and empty weight are usually too high for the majority of these aircraft to reach or maintain FL510 for any useful length of time.

We operate a Global Express and similar to the G-IVSP that I used to fly, we target FL390-FL410 as our initial cruise altitude, step climbing several hours later to FL450. ISA and weight are the two controlling factors. The Global wing is optimized at M0.83, with normal cruise at M0.85 - long range cruise is usually a function of optimum TAS, but can be as slow as M0.77 for a 12 + hour leg.