V-NAV on 747-400

[Eziocin 46]

Recently experienced quite a strange behaviour of the 747-400. Descending from cruise altitude V-NAV, L-NAV, A/P ON, I switched to Level Change and then shortly after I resumed V-NAV. After returning to V-NAV my target IAS dropped to 100 Kts and the AP started to slow down the aircraft. Tried again several times and evry single time I had the same story: switching from V-NAV to a different descent mode and then returning to V-NAV cause the target IAS to drop to 100 Kts...!Am I doing something wrong or is it a known bug ?Apart from this the Queen is a lovely aircraft..!Regards

[Guest Buck Bolduc]

>Recently experienced quite a strange behaviour of the>747-400. Descending from cruise altitude V-NAV, L-NAV, A/P ON,>I switched to Level Change and then shortly after I resumed>V-NAV. After returning to V-NAV my target IAS dropped to 100>Kts and the AP started to slow down the aircraft. >Tried again several times and evry single time I had the same>story: switching from V-NAV to a different descent mode and>then returning to V-NAV cause the target IAS to drop to 100>Kts...!>Am I doing something wrong or is it a known bug ?>Apart from this the Queen is a lovely aircraft..!>>RegardsI think what your doing is changing from VNav Path to VNav-Speed profile.If I understand you correctly.

[Guest neeraj.pendse]

Along the lines of what Buck is saying, can you note and tell us what VNAV mode you are in when AP starts to decelerate? I am sure you know this, but really on the new Boeings one has to look at the PFD to make sense of what the AP is doing, MCP does not give you all information. Is the Speed in MCP window set to 100 kts by default/ when this happens? What is the autothrottle mode when this happens? ARM?, MCP-SPEED?Let us know. - Neeraj.