Maximum service ceiling

What is the maximum service ceiling of the Dash 8 Q 400 with PW 150 engines? There are hints, that it is at FL 270 instead of FL 250. What is definitiv correct?

Greetings
Ingo

Comments

  • 27,000 ft

  • edited March 11

    It is FL250 without 10 minute emergency oxygen masks for each passenger.

    It is FL270 for the few Q400 equipped with pax emergency oxy (I think Horizon is one such operator). Such a modest altitude increase is probably why few operators have specified them.

    There's probably sufficient engine power remaining to go above FL300 but I think you reach the pressure differential limit for the fuselage with an 8000 ft cabin altitude at FL270, so going higher would mean oxygen cylinders and masks for everyone aboard. It should be noted Majestic's simulation does not continue simulating decreasing performance above FL270 so you can't realistically fly this out of envelope situation using it.

    ckyliu - Proud supporter of http://www.ViaIntercity.com, 950+ flights for J41 & Q400 and 200+ for A320

  • Please confirm hypoxia is simulated in the MJC model?
    I wasn't aware it was, hence 27000 ft (Service Ceilings are normally given in absolute altitude, not Flight Level).

  • edited March 13

    Hypoxia simulation is irrelevant to the service ceiling, which is a real life certified value and not something specific to the sim. Service ceiling is based on climb rates and stall/speed buffet margins from flight testing in a clean configuration, then system and regulatory limitations such as oxygen provision; perhaps you're getting confused with the absolute ceiling which is essentially the highest altitude level flight can be sustained (as I already explained this will be much higher in the Majestic because it doesn't continue simulating thinning air much above FL270)?

    ** As I already clearly stated, it is the provision of emergency passenger oxygen (specifically of at least 10 minutes capacity for each passenger) that permits a service ceiling of 27000 ft **

    Service ceilings are NOT given in "Absolute altitude" as that is AGL (aka height), it will be "pressure altitude" which is uses a standard datum (1013hPa/29.92inHg in ISA conditions, aka Flight Level, although a temperature correction may be provided) or "density altitude". I used flight level because that's how the OP asked, but we all know how flight levels translate to feet.

    ckyliu - Proud supporter of http://www.ViaIntercity.com, 950+ flights for J41 & Q400 and 200+ for A320

  • Hi,

    Thank you got that Brief explanation.Wasn't aware, that this is more an oxygen issue.

  • The definition of a service ceiling is the maximum height at which a particular aircraft can maintain a defined rate of climb... Nothing whatsoever to do with hypoxia or pressurisation or any other ability other than engine/airframe capability - which is why it's specified in pressure altitude. Separation of church and state as it were...
    Now, it might be different in the individual case like the Dash 8-400 where the equation also needs to consider the self-loading cargo and their physical requirements. This may be the case here, where the graphs cross at FL250.
    In effect the OP asked the wrong question, albeit unwittingly. Very interesting answers, though and I wonder how many aircraft are like the -400 and performance limited by ancillary systems?

  • edited March 15

    Trust you to make it someone else's fault... Anyway, most jetliners are limited by the regulatory 8000 ft cabin altitude (thus declared service ceiling is dependent on what pressure differential the fuselage will reliably withstand) so the Q400 is hardly an individual case, for example:
    Ceiling B747 = 45,100 feet (cabin altitude at 8,000 feet)
    Ceiling B707 = 41,000 feet (cabin altitude at 8,000 feet)
    Ceiling B727 = 41,000 feet (cabin altitude at 8,000 feet)
    Ceiling B73G = 41,000 feet (cabin altitude at 8,000 feet)
    Ceiling Learjet 31A = 51,000 feet (cabin altitude at 8,000 feet)
    Ceiling Concorde = 61,000 feet (cabin altitude at 8,000 feet)
    There are accounts of both the 747 and Concorde being flown much higher than the above so the airframe and engines are certainly capable of sustaining more altitude. It's only recently that manufacturers have offered lower cabin altitudes at service ceiling, predominantly in the business jet sector.

    There is also a descent requirement, I think they must be able to get a 14,000 ft cabin altitude within 4 minutes of probable decompression events. That's why production Concorde aircraft have much smaller windows than the earlier prototypes, otherwise they'd have to improve the aircraft's descent rate to retain a 61000ft within that rule.

    (And before any hairs are split on the above, the FAA has had stricter requirements regarding exposure to high cabin altitudes during decompression for decades now and it limits most new types to under 41,000ft ceiling. I believe unpressurised emergency oxygen is ineffective above FL430 too)

  • In my DA42 / DA62 we have no such limits. FAA or CAA, nor ANO or EASA. Purely an aircraft/performance limit. Even oxygen-equipped.
    An addendum for pressurised/oxygen-equipped aircraft, or some other bollox exclusive to the FAA, I wonder?

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