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Crknyj86

SID altitude restriction problem

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I am having problems using the autothrottles with SID that require you to stay below certain altitudes. For example the OSHNN4 out of LAX. When I fly the approach manually but with autothrottles engaged, I initially pitch to maintain speed as the FMC shows and followed the flight director. The first time I blew threw the altitudes. The second time I lowered the pitch to slow my ascent but I end up accelerating way past 250 kts while the autothrottles stay at climb power. As of now the only way to fix this is to disengage the autothrottles.

I was wondering if there is anyway to fix this so that the autothrottles will reduce trust to keep the speed under 250kts and keeping below the altitude restriction. Any help would be appreciated.

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Set the Alt restriction (3000 ?) in the MCP ALT window.

After climb thrust reduction altitude (1500 feet-ish) select a climb mode... eg dial 250 on the speed panel, then pull the ALT knob and pull the SPEED knob. This will give you a "Level change" climb at climb thrust and flight director indications to maintain a speed of 250 KIAS. When you reach your Alt restriction the FD will command level flight and the A/T will automatically change to speed mode...to maintain level flight at 250 KIAS.

 

You can achieve the same result if you load the departure, with its speed and altitude constaints into the FMC before takeoff. Then arm PROF and NAV before t/o. Same result as above, except less work for you ... no need to choose a climb mode..... when you arm PROF the A/T will change to climb thrust at 1500 ft above airport elevation.

 

I am still new to the MD-11 so I think the above is corect.


Peter Schluter

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Welcome to AVSIM!

 

If the flight management system of the MD-11 is anything like that of Boeing aircraft, ensure that you have specified altitude and speed restrictions (i.e., confirmed that they are hard restrictions instead of estimated values). Also remember that the aircraft will command a climb speed greater than 250 kt, usually at heavier weights, if the minimum clean speed of the particular aircraft configuration is greater than 250 kt.


Regards,
Owen
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