Ceiling (aeronautics): Difference between revisions

Service ceiling is wherethe density altitude at which the rate of climb drops below a prescribed value.

The '''service ceiling''' is the maximum usable altitude of an aircraft during normal operations. Specifically, it is the [[density altitude]] at which flying in a [[clean configuration]], at the best [[rate of climb]] [[airspeed]] for that altitude and with all engines operating and producing maximum continuous power, will produce a given rate of climb. A typical value might be {{cvt|100|ft/min|m/s}} climb,<ref name=PHAK>{{cite book |url=http://www.faa.gov/regulations_policies/handbooks_manuals/aviation/pilot_handbook/media/PHAK%20-%20Chapter%2010.pdf#page=7 |chapter=10: Climb Performance |archive-url=https://web.archive.org/web/20150625110258/http://www.faa.gov/regulations_policies/handbooks_manuals/aviation/pilot_handbook/media/PHAK%20-%20Chapter%2010.pdf |archive-date=2015-06-25 |page=10-7 |publisher=[[FAA]] |title=Pilot's Handbook of Aeronautical Knowledge (FAA-H-8083-25A)}}</ref> or on the order of {{cvt|500|ft/min|m/s}} climb for jet aircraft.

The one-engine inoperative (OEI) service ceiling of a twin-engine, [[fixed-wing aircraft]] is the density altitude at which flying in a clean configuration, at the best rate of climb airspeed for that altitude with one engine producing maximum continuous power and the other engine shut down (and if it has a propeller, the propeller is feathered), will produce a given rate of climb, usually {{cvt|50|ft/min|m/s}}.<ref>{{cite book |url=https://www.faa.gov/regulations_policies/handbooks_manuals/aviation/airplane_handbook/media/14_afh_ch12.pdf |title=Airplane Flying Handbook (FAA-H-8083-3B) |last= |first= |publisher=[[FAA]] |year=2016 |isbn= |location= |pages=12–19 |chapter=12: Transition to Multiengine Airplanes |quote= |via=}}</ref>

Most commercial [[jet airliner|jetliners]] have a service (or certificatedcertified) ceiling of aboutunder {{cvt|4245,000| ft|km mi}}(13,700 m)<ref>{{Cite web|last=Cox|first=John|title=Ask the Captain: Highest altitudes for planes|url=https://www.usatoday.com/story/travel/columnist/cox/2017/05/28/altitude/102185856/|access-date=2020-11-06|website=USA TODAY|language=en-US}}</ref> and some [[business jets]] about {{cvt|51,000|ft|km mi|1}}.<ref>See e.g. [http://www2.bombardier.com/en/3_0/3_2/3_2_3/3_2_3_2_3.jsp?pageid=3_2 Bombardier Global Express XRS Specifications] {{Webarchive|url=https://web.archive.org/web/20100223011423/http://www2.bombardier.com/en/3_0/3_2/3_2_3/3_2_3_2_3.jsp?pageid=3_2 |date=2010-02-23 }}.</ref> Before its retirement, the [[Concorde]] [[supersonic transport]] (SST) (as well as the [[Tupolev Tu-144]] before it was retired) routinely flew at {{cvt|60,000|ft|km mi|1}}.

The '''absolute ceiling''' is the highest altitude at which an aircraft can sustain level flight. Due to the thin air at higher altitudes, a much higher [[true airspeed]] (TAS) is required to generate sufficient lift on the wings. The absolute ceiling is therefore the altitude at which the engines are operating at maximum [[thrust]], yet can only generate enough lift to match the weight of the aircraft. Hence, the aircraft will not have any excess capacity to climb further. At absolute ceiling, the aircraft can no longer accelerate, since any acceleration will lead to higher airspeed and therefore excess lift. Stated technically, it is the altitude where the maximum sustained (with no decreasing airspeed) [[rate of climb]] is zero.

Compared to service ceiling, the absolute ceiling of commercial aircraft is much higher than for standard operational purposes. In the [[Concorde]]'s case, it was tested to be {{cvt|68,000|ft|km mi}}. It is impossible to reach for most (because of the vertical speed asymptotically approaching zero) without [[afterburner]]s or other devices temporarily increasing thrust. Another factor that makes it impossible for some aircraft to reach their absolute ceiling, even with temporary increases in thrust, is the aircraft reaching the "[[coffin corner (aviation)|coffin corner]]". Flight at the absolute ceiling is also not economically advantageous due to the low [[indicated airspeed]] which can be sustained: although the [[true airspeed]] (TAS) at an altitude is typically greater than indicated airspeed (IAS), the difference is not enough to compensate for the fact that IAS at which minimum drag is achieved is usually low, so a flight at an absolute ceiling altitude results in a low TAS as well, and therefore in a high fuel burn rate per distance traveled. The absolute ceiling varies with the air temperature and, overall, the aircraft weight (usually calculated at [[MTOW]]).<ref name=PHAK/>