more questions on the fms B737

[Torstennnn]

more of these jar fcl questions - where I can find contradictory answers im my theory trainer aviationexam

they'd ask me:

1.: if the fms aligned in nav or align mode
never having seen one in reality i'd say in align mode

2.: and they claim that the fms b737/800 used dme/dme only for position fixing -
i heard it used dme/vor as well

3.: and they claim that the fms calculating areanavigation based on dme/vor could not provide information about winddirection and velocity

does anybody happen to know?

[Rainboe]

Torsten, my thoughts:
1- aligns in Align mode, then you switch it to Nav. However, you can simply switch straight to Nav, and it will run through its align mode then automatically engage Nav
2- Aircraft equipped with GPS can use GPS/GPS for position fixing, which is very accurate-I thought all B737 700-900 had this. The next most accurate mode is DME/DME. Then VOR/DME although this is not very accurate.
3- not sure. I think it will still give a wind vector, although it may be inaccurate.

[sameep]

This is from the 737 NG manual. Hope it helps

In flight, the FMC position is continually updated from the GPS, navigation
radios, and IRS. Updating priority is based on the availability of valid data from
the supporting systems.
FMC position updates from navigation sensor positions are used in the following priority order:

• GPS
• two or more DME stations
• one VOR with a collocated DME
• one localizer and collocated DME
• one

Radio position is determined by the intersection of two DME arcs. If the DME radios fail, or if suitable DME stations are not available, FMC navigation is based on IRS position information only.

[Todders]

sorry to be a pain but sometime it's matters in jar my little bit.

1. It's the IRS that aligns not the FMS. Also more relivently i'm almost sure (having done jar's about 3 years ago) the jar ans to that is in NAV mode this is the normal way to do it in operations unless you are short on time.

2. As above can't do better than that.

3. As for wind vector not sure to be honest nothing in the boeing ops manual. But as far as i'm aware it's is driven by the IRS therefore unless you lose both of them i't should be there hopefully someone else can correct me if wrong. Only time it blanks is if the velocity drops below 4kts, if you havent experienced more than 6kts yet or your TAS is less than 101kts.