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Joined: Sun Jul 01, 2001 1:52 am

747 Classic Autopilot/Autothrottle

Wed Jun 18, 2003 11:24 pm

Hi All,

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Photo © Berni Lüdtke

In the photo above of a Lufthansa 742 Freighter the autothrottle knob on the glareshield is set at the off position, but the annunciator above the airspeed indicator is showing MACH mode, and there doesn't seem to be a MACH mode on the knob anyway - how is the MACH mode set and autothrottle Mach number changed?

Also there is a v/s mode on the knob - does this control vertical speed regardless of airspeed or will it vary pitch attitude to maintain the airspeed set in the IAS window during climbs and descents at current engine power setting?

As always any and all help appreciated.


Statistically, people who have had the most birthdays tend to live the longest.
Posts: 178
Joined: Mon Nov 06, 2000 5:29 am

RE: 747 Classic Autopilot/Autothrottle

Thu Jun 19, 2003 12:39 am

Hi Gordon,

The switch you are reffering is not the A/T one. It handles the "vertical navigation" from the aircraft. If you switch it to V/S, your climb or descend will be controlled with the V/S wheel on the MCP. In IAS the AP will hold the selected airspeed with VS.

The master ON/OFF Autothrottle switch is on the left side of the MCP. http://planeta.terra.com.br/relacionamento/dule/mcp1.jpg  Big grin

Posts: 613
Joined: Sun Dec 10, 2000 7:33 am

RE: 747 Classic Autopilot/Autothrottle

Thu Jun 19, 2003 12:35 pm

I beleive mach hold just holds whatever mach you're presently at when it's engaged.
Indianapolis, IN

RE: 747 Classic Autopilot/Autothrottle

Thu Jun 19, 2003 11:57 pm

Hello Gordon and friends -
That switch on the "P-10" panel (glareshield panel with all A/P controls) is called the SPS Speed Mode Switch - has the following positions -
TURB - Used for turbulence penetration with A/P in MAN only, provides for A/P commands with reduced gain (i.e. not "chasing" altitude set)...
OFF - self explanatory
V/S - Used in conjunction with vertical speed control (a vertical white rotary knob) permitting to set vertical speed from 4,000 fpm climb to 8,000 fpm descent...
PMS (option) - If aircraft has PMS (older form of FMS), the pitch axis will control the aircraft as per levels and speeds programmed in PMS... In cruise, this position permitted the aircraft (on ALT HOLD) to vary slightly on altitude, some +200 to -200 feet... to keep speed/Mach... this is NOT USED in RVSM airspace, because outside of altitude tolerances...
IAS - Controls pitch axis referenced to CAS existing at engagement... generally used by pilots for cruise climb and descent...
MACH - Controls pitch axis referenced to indicated Mach at engagement... could be used for climb/descent at higher levels, generally above FL280 or so, but rarely used by pilots, since that pitch axis control seems to "chase" the set Mach number in all airplanes I personally flew...
Happy contrails -  Smile
(s) Skipper

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