Service Ceiling vs. Max Operating Altitude
- Thread starter Coney
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flyguy
Well-Known Member
Service ceiling is the maximum altitude where a 100 foot per minute climb can be maintained. Above the service ceiling you should still be able to climb, but climb performance will be less than 100 feet per minute. Max operating altitude is the maximum altitude it will go. Both are theoretical as there are many factors that would deturmine the actual values.
Alchemy
Well-Known Member
From the FAR part 23, the definition of Maximum Operating Altitude:
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(a) The maximum altitude up to which operation is allowed, as limited by flight, structural, powerplant, functional or equipment characteristics, must be established.
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Typically, maximum Operating Altitude is the highest the plane can go for structural/pressurization reasons. For instance, FL370 is our Maximum Operating Altitude in the ERJ because that's the highest we can go will maintaining a 7.8 psi cabin differential pressure while also maintaining an acceptably low cabin altitude (8000 ft), even though the engines and aiframe would have no problem climbing higher if the cabin altitude was not an issue.
Service ceiling, on the other hand, as flyguy said is the maximum altitude at which the airplane can maintain at least a 100 fpm rate of climb with all engines operating.
Absolute altitude is the highest altitude the airplane can reach, period.....in other words you're hanging on at Vy with a 0 fpm rate of climb. Maximum Operating altitude is usally not the same number....MOA is more of an equipment limitation than a performance limitation.
[ QUOTE ]
(a) The maximum altitude up to which operation is allowed, as limited by flight, structural, powerplant, functional or equipment characteristics, must be established.
[/ QUOTE ]
Typically, maximum Operating Altitude is the highest the plane can go for structural/pressurization reasons. For instance, FL370 is our Maximum Operating Altitude in the ERJ because that's the highest we can go will maintaining a 7.8 psi cabin differential pressure while also maintaining an acceptably low cabin altitude (8000 ft), even though the engines and aiframe would have no problem climbing higher if the cabin altitude was not an issue.
Service ceiling, on the other hand, as flyguy said is the maximum altitude at which the airplane can maintain at least a 100 fpm rate of climb with all engines operating.
Absolute altitude is the highest altitude the airplane can reach, period.....in other words you're hanging on at Vy with a 0 fpm rate of climb. Maximum Operating altitude is usally not the same number....MOA is more of an equipment limitation than a performance limitation.
MidlifeFlyer
Well-Known Member
[ QUOTE ]
From the FAR part 23, the definition of Maximum Operating Altitude:
[ QUOTE ]
(a) The maximum altitude up to which operation is allowed, as limited by flight, structural, powerplant, functional or equipment characteristics, must be established.
[/ QUOTE ]
..MOA is more of an equipment limitation than a performance limitation.
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And that's they key to a real difference. MOA is an operating limitation. Service ceiling is not - just some information about expected performance.
From the FAR part 23, the definition of Maximum Operating Altitude:
[ QUOTE ]
(a) The maximum altitude up to which operation is allowed, as limited by flight, structural, powerplant, functional or equipment characteristics, must be established.
[/ QUOTE ]
..MOA is more of an equipment limitation than a performance limitation.
[/ QUOTE ]
And that's they key to a real difference. MOA is an operating limitation. Service ceiling is not - just some information about expected performance.
ananoman
New Member
There are lots of certification issues for operating at high altitudes. Part 25 aircraft (Transports) have to keep an 8,000' cabin and may be limited by the max cabin differential mentioned above.
There may be other issues as well. If you want to go above FL410 and have rear mounted engines, they must be behind the pressure vessel, so an uncontained failure does not cause a depressurization. The Hawker 800 is limited to FL410 for this reason. The same aircraft certified under different rules in Britain can go to FL430. Some business jets have an aft baggage compartment that may be accessable in flight, but they are equipped with a second pressure bulkhead in front of the engines that must be sealed above a certain altitude.
There is also the requirement to be able to do an emergency descent to 15,000' from max operating altitude in 4 minutes. So, if you have a hydraulics failure, the checklist may require a descent to a lower altitude. The hydraulics system may have no effect on flying qualities, but if you have hydraulic speed brakes that are necessary to meet the descent requirement, then you must descend to a lower altitude to comply with the 4 minute rule. Other smaller Part 23 aircraft like the Meridian are limited to FL250 due to the extra systems required to fly higher. It is possible to certify aircraft to FL250 without an oxygen system for the passengers if it can perform an emergency descent quick enough (the pilot needs only be provided with an emergency supply that can be met by a chemical oxygen generator) and other redundant items like double pane windows.
There may be other issues as well. If you want to go above FL410 and have rear mounted engines, they must be behind the pressure vessel, so an uncontained failure does not cause a depressurization. The Hawker 800 is limited to FL410 for this reason. The same aircraft certified under different rules in Britain can go to FL430. Some business jets have an aft baggage compartment that may be accessable in flight, but they are equipped with a second pressure bulkhead in front of the engines that must be sealed above a certain altitude.
There is also the requirement to be able to do an emergency descent to 15,000' from max operating altitude in 4 minutes. So, if you have a hydraulics failure, the checklist may require a descent to a lower altitude. The hydraulics system may have no effect on flying qualities, but if you have hydraulic speed brakes that are necessary to meet the descent requirement, then you must descend to a lower altitude to comply with the 4 minute rule. Other smaller Part 23 aircraft like the Meridian are limited to FL250 due to the extra systems required to fly higher. It is possible to certify aircraft to FL250 without an oxygen system for the passengers if it can perform an emergency descent quick enough (the pilot needs only be provided with an emergency supply that can be met by a chemical oxygen generator) and other redundant items like double pane windows.
Alchemy
Well-Known Member
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Ahh yes. I was confusing maximum operating altitude with absolute altitude. Good catch.
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Well, I'll have to correct myself this time, I should've said absoulte ceiling, not absolute altitude.
Absolute Altitude is your another way of saying AGL, not relevant to this discussion.
Ahh yes. I was confusing maximum operating altitude with absolute altitude. Good catch.
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Well, I'll have to correct myself this time, I should've said absoulte ceiling, not absolute altitude.
Absolute Altitude is your another way of saying AGL, not relevant to this discussion.
flyguy
Well-Known Member
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Ahh yes. I was confusing maximum operating altitude with absolute altitude. Good catch.
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Well, I'll have to correct myself this time, I should've said absoulte ceiling, not absolute altitude.
Absolute Altitude is your another way of saying AGL, not relevant to this discussion.
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Another good catch.
I've got a really stupid memory aid remembering the difference between absolute altitude and true altitude. I used to think they were the other way around, so I remembered absoute (vodca) is a liquid so absolute altitude is above sea (also a liquid) level. It was such a great way to remember it that I didn't want to let a little thing like it being completely backwards ruin it, so when I learned it was the other around I just remembered the same thing but just backward.
Told you it was stupid, but it works for me.
[ QUOTE ]
Ahh yes. I was confusing maximum operating altitude with absolute altitude. Good catch.
[/ QUOTE ]
Well, I'll have to correct myself this time, I should've said absoulte ceiling, not absolute altitude.
Absolute Altitude is your another way of saying AGL, not relevant to this discussion.
[/ QUOTE ]
Another good catch.
I've got a really stupid memory aid remembering the difference between absolute altitude and true altitude. I used to think they were the other way around, so I remembered absoute (vodca) is a liquid so absolute altitude is above sea (also a liquid) level. It was such a great way to remember it that I didn't want to let a little thing like it being completely backwards ruin it, so when I learned it was the other around I just remembered the same thing but just backward.