Holding Pattern

[CubanPete 0]

Hi all!I've a little question about holdings. Yesterday I tried to perfom a holding with the FMC. The FMC displayed 265KTS as best speed. I changed vom VNAV to SPEED and entered 265 in the MCP. The planes reduced the speed to 265, but it didn't follow the flight path for the holding. There were a couple of miles between me and the planned flight path. My question: when 265 obviously the best speed, what is the best speed for the pattern?All the bestPeter Burghardt

[krazyk 157]

Hi Peter,If you're following procedures then there are set rules on holding speeds and patterns which can be accessed through charts. Generally, as a rule, Up to 14,000 ft Normal Condition - 230 Kts and Turbulence Condition - 280 ktsAbove 14,000 ft to 20,000ft Normal Condition - 240 kts and Turbulence Condition - 280 ktsAbove 20,000ft to 34,000 ft Normal Condition - 265 kts and Turbulence Condition - 280 kts or 0.8 Mach, whichever is lessAbove 34,000 ft Normal and Turbulence Condition - 0.83 MachThe speed that the FMC calculates and is then displayed on the CDU is the most cost effective speed and NOT the one it wants you to fly at.Depending on how fast you are and how you've configured the CDU for your hold will determine your rate of turn which will be a Rate 1 turn (3 degrees/second) or 25 degrees bank angle - whichever is less. The timing of the inbound/outbound leg depends on what height you're flying the hold. Usually, a minute below 14,000 ft and a minute and a half above.Hope this helps :)Cheers,

[yos233 1]

The holding logic does not begin until after the first turn. The hold that is depicted on the flight path is a placer image, and will enlarge itself to your turn radius after you are on the "downwind" leg. It will then continue to reshape itself as your turn radius changes between holding cycles. The placer image is just to small for a 747 to turn in.

[CubanPete 0]

The holding logic does not begin until after the first turn. The hold that is depicted on the flight path is a placer image, and will enlarge itself to your turn radius after you are on the "downwind" leg. It will then continue to reshape itself as your turn radius changes between holding cycles. The placer image is just to small for a 747 to turn in.

I've observed this behavior, but the 744 even didn't follow the reshaped path.

[tipitout 5]

I often encounter odd holding behavior where the hold is pre-programed as part of a STAR. What I find helps is to delete the STAR hold, then enter it again manually. If I do this then the plane follows the hold flawlessly first time, every time.