View Full Version : FMS Collins 4200 on CRJ900 during cruise

8th Dec 2006, 08:51
May I have your opinion on handling the FMS Collins 4200 during cruise on the CRJ900. Actually during cruise, I was putting data about OAT and wind by legs from the comuterised flt plan into the PERF page as it is enabled. It helps to fine tune the elements of TOD etc. I has doing that on previous acf types (like B737-400...). But the TRI has told me that we are not supposed to do that and that it was a bad negative transfer from previous aircraft types. On the CRJ900, he said, that is not needed.

We are still operating under Bombardier so called SOP, because there is no other in use. That issue is not exercised in that SOP.That issue is not exercised in that SOP at all.

I am looking for your opinion about that?



10th Dec 2006, 02:53
During initialization, on PERF INIT page 2, you may input forecast wind for Climb, Cruise, Descent along with forecast ISA deviation. This is input as MXXX for headwind, and PXXX for tailwind and XX or -XX for temp. Keep in mind, our dispatch uses flight planning software that computes an average wind component for each phase. We just enter that from the dispatch directly into the FMS during preflight.

As far as leg winds are concerned, I can only say my company's SOP does not call for updating on a leg-by-leg basis, probably because we enter averages for the flight. Also, the FMS is constantly updating itself by sending the input forecast wind and actual sensed wind through an algorithm.

Keep in mind that as you stay in cold air, the indicated fuel quantity will usually decrease below FMS fuel quantity. I have seen up to 600 lbs difference in cruise. It is our company SOP to NOT update fuel quantity during flight for this reason. The last time we update FOB is prior to pushback.

I'm sure I've been not much help. Enjoy.

As always, follow your company SOP.

Elliot Moose
10th Dec 2006, 18:16
The information on Perf Init page 2 works very well for shorter legs where fuel burn isn't so critical. It just plugs in the average for the three phases of flight. On longer legs where the winds will change considerably over the course of the trip (I do it when crossing the Atlantic on ferry flights, etc) it is much better to put in the wind for each leg. For most airline ops, either one is okay--just don't do both or the last one entered will prevail. I have no idea why one would be prohibited from using it.

Firesysok is correct in that the FMS uses a complex algorithm to meld present actual winds with the "predicted'" stuff that you put in either in the leg winds or the perf init. Basically it uses 100% actual at the aircraft position and gradually tapers down until it is using 100% predicted some 200nm ahead of present position. If your company is only doing 400-600nm legs, there isn't much point in trying to put each leg wind in when you will only be level for a couple hundred miles!:hmm:

12th Dec 2006, 14:24
Thanks for all the answers. I was actually meaning that if I do not put the average wind and temperature for climb cruise and descent during FMS init phase, is it ok if I use the predicted ones from the computerized flt plan concerning wind and temperature? I know that I can do that during init phase, but I was wondering if it is ok during flt also?

Elliot Moose
13th Dec 2006, 23:56
Doing it after airborne is no problem either. I do it a lot of the time when I'm looking at a long leg after a short turn around. Again the FMS will still use that sliding algorithm out to 200nm, so the first bit won't usually have too much effect. If you're really stretching range though, it's best to do on the ground so you can look at the predicted fuel at landing before you take off.