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4 Answers

Altitude and Speed

Asked by: 6179 views ,
General Aviation

Is there a chart that shows maximum true air speed (TAS) for a large commercial plane 737 or larger at different altitudes? If not what is the TAS for one of those planes under 1000ft? Thank you for your time-Brian

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4 Answers



  1. John A Lindholm on Mar 24, 2011

    A jet transport aircraft does not have a maximum TAS at altitude.  It has a maximum certified mach number as Vmo, not an airspeed.
     
    The TAS will vary with temperature….  most often discussed in relation to ISA.  When temperatures are colder than normal, an aircraft operating at its maximum Vmo mach will have a slower TAS than the when its operating in warmer than normal temperatures at the same mach number. 

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  2. John A Lindholm on Mar 24, 2011

    Brian…..  to further expand my answer, the maximum Vmo at lower altitudes (the transition on most aircraft from mach to a TAS Vmo is usually near FL280) varies greatly and sometimes changes or has several values at different altitude blocks.  At the most low altitudes, the Vmo airspeed restriction is usually determined by the windshield’s ability to handle the certification bird strike criteria.  In many parts of the world, the ATC airspeed restrictions allow an IAS above 250 kts, so many transport jets are capable of a TAS as high as 400+ kts at very low altitudes, should they choose to operate at that speed.  In some ATC environments, the arriving aircraft will have different IAS limitations than the departing aircraft have.  These airspeeds are always given as IAS even though most jets have a TAS readout.  The automated flight control systems use IAS for constant airspeed climbs or descents, for instance.
     
    Lastly, TAS is not the active determination for speed for overwater operations, mach is.  Aircaft are separated by flying a constant mach, not a TAS.  IAS is very poor for flight restriction at high altitudes as an aircraft flying a TAS of 460 kts might have an IAS in the low 200s.
     
    Hope this helps

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  3. John A Lindholm on Mar 24, 2011

    Brian….  another comment/correction:  My previous statement “It has a maximum certified mach number as Vmo, not an airspeed.”  should state maximum certified mach number as Mmo, not Vmo.   Vmo is airspeed as IAS, Mmo is indicated mach value, not IAS.
    Also, you did ask “is there a chart”…..  the most correct answer is that there is a calculation to determine what the maximum TAS would be at a given altitude, temperature and mach number.  This can be done by charting and with newer jets, by calculation with an electronic device.

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  4. Wes Beard on Mar 24, 2011

    The fastest the B-737 is certified for at 1000ft MSL is 340 kts calibrated which is awfully close to the KTAS speed.  John is correct about using mach or Mmo at altitude.  The fast mach number for the B-737 is .82 mach.
     
    The airplane usually above 10,000ft MSL can cruise at Vmo.  The plane can climb at Vmo till it reaches the Mmo value, the plane will then have to slow down as it continues to climb to stay at a constant mach number.
     
    In the performance pages for the jet that I fly shows different mach numbers with weight, temperature and pressure altitude as factors.  When you get the combination you want, the performance chart will return KTAS, %N1 and Lb/Hr/Eng.  For example, you are cruising at .80 at FL350 with a 30,000 lb airplane at ISA.  The performance numbers are 461 KTAS, 87.9 %N1 and 1071 lb burn per hour for one engine.

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