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Robi77

FMC question

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In the PMDG-747-400 FMC there are 2 entries in the VNav page which I donot quite understand.1) SpeedTrans2) SpdRestWhat are the differences between the two since to me they seem to do the samething.Ex: I want to fly at a max speed of 250 knots up to 10000 feet. I found out that both options do the same thing and now I wonder when to use what ?ThanksHerbert Werni

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Hi Herbert,Speed Trans is the altitude and speed restriction set before reaching the stated transition for the specific airport.This is usually found on the airport navigation charts.As you said, in the US it's usually 10,000ft and 250 kts not to be exceeded. For Europe and elsewhere it's different. This is the altitude where the altimeters are reset.For the other option, this SPDRest stands for Speed Restriction and is another entry in the FMC that can be used by the pilot to add an additional speed restiction e.g if there was a specific ATC instruction to climb to an intermediate altitude on the climb and speed was also restricted at that level.Hope that helps,Regards,


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Hi Herbert,Speed Trans is the altitude and speed restriction set before reaching the stated transition for the specific airport.This is usually found on the airport navigation charts.As you said, in the US it's usually 10,000ft and 250 kts not to be exceeded. For Europe and elsewhere it's different. This is the altitude where the altimeters are reset.
Speed Transition does as you say limit the SPD to 250kts below 10000ft, unless the aircraft weight requires a higher clean speed than 250kts...this is based on additives to VREF30 & at very high weights can be near to 280kts...hence in the US & Canada all 744s & other heavy metal add 'heavy' to their callsign...which also indicates the wake category that the aircraft is in.It is not 'where the altimeters are reset'The Transition Altitude is entered on the right side of the VNAV CLB page as Xxxxft...18000 in the US & Canada...& country specific.

Steve Bell

 

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