Rod

[ronnie123]

Any help if there are formulae for ROD.

thks

[Genghis the Engineer]

Many, what are you actually trying to achieve?

G

[ronnie123]

To get ROD from TOD. Also how do the big jets do it without FMS and VNAV.:confused:

[QAVION]

"To get ROD from TOD. Also how do the big jets do it without FMS and VNAV."

Sounds like you're a desktop sim pilot, Ronnie? If so, you may get a better answer to your question on a website dedicated to the sim you are using. Not all desktop sims reflect reality so you may have to operate your simulated aircraft a little differently from a real aircraft to get the desired result. There are some excellent forums on the avsim.com website, for example, which may provide some guidance in this area.

For info: The FMC computes a vertical path from TOD with the engines at idle (for a considerable portion of the descent) and at an airspeed/mach dependent on how economical a flight you are making. V/S is only a side effect of these two and would vary as the airplane descended: V/S mode on a modern glass cockpit aircraft would only be used in specific circumstances. Depending on ATC restrictions, pilots may follow a similar idle descent path (for maximum economy). Of course, the decent path taken would be dependent on the Autopilot modes available (FLCH, V/S, etc). Does your simulator have these modes?

For an idle descent to the ILS Glideslope... allowing for levelling off and slowdown... you could probably guestimate your TOD point (distance from your destination airport) by multiplying your altitude (in thousands of feet) above the airport by 3 and then adding 10~15nm. Some aircraft may be more slippery than others and there may be headwinds or tailwinds, so you may have to adjust this value accordingly. It can be an "art" as well as a science.

Some aircraft navigation displays have what is sometimes called a "green banana" which will give you a rough idea of where (on earth) you will reach the altitude selected on your autopilot control panel for the current vertical speed (whatever it may be). However, it won't allow for things like slowing down from descent speed to approach speed.

Hope this helps.

Rgds.
Q.