How many decimal places please.
 

Would be grateful if you could advise me how many decimal places are used when flight crew are putting in "the numbers" into the flight computer..some call this the flight management system. In particular I am interested in the fuel amount in weights...strictly termed, the mass of fuel. Will it accept litres also, and is there a "conversion button" to quickly skip from metric to non metric..viz pounds weight? Or U.S. gallons volume to UK gallons volume?

Our loadsheet is provided to the nearest kg. There is no facility to put decimals in for weight.

We tend to round up to the neares 100kg eg a zero fuel weight of 26343kg would be entered as 26400kg.

On the issue of fuel, the FMS speaks to the fuel gauges. It is possible to enter a fuel figure manually, but it is done rarely - normally you would only do it if you enter the ZFW before the a/c has been refuelled.

Fuel gauges read to the nearest 10kg on the a/c I fly.

Decimal points are used for stabilser trim settings and flight path angles and not much else.

There is a page on our FMS that allows us to work out that a 10663ft runway is 3250m long and do other conversions, but we do not mix units.

A weight is kg, fuel qty is kg, altitude is ft, speed is kts, pressure is mbar (or psi for hydraulics)

Thanks for the reply.

Only two things that arise. I know in Russian Federation they use metres for flight levels. I don't know what the former east Bloc uses these days.

For pressure I think some quote "kiliopascals" is that the same a BAR?

Also in the USA all barometrics are given in "inches mercury". I wonder if say the barometric input has a built in conversion from BAR to kPa to inches?

Usually we work to the following

1 Bar =
1000 mBar =
1 Atmosphere =
101300 Pa =
101.3 kPa =
760 mmHg =
14.7 psi

Hope this helps

Conversions
 

Well this would really annoy me.

Is there not a switch somewhere on the dashboard..something that will immediately show up as all metric or just bits of it?

NO!
ICAO Annex 5 gives the following conversion factors:
1 bar = 100,000 Pa
1 millibar = 100 Pa

standard pressure is therefore 1013 hPa = 1013 mbar

Zipping back to the start of the thread, reasonable accuracy regarding fuel is all that is required. For the last 13-14 years or so, I've only ever used kilos except for when you write up the trip paperwork where you enter the litres uplifted.

On the bug smashers I fly, the flight plan contains numbers to the nearest whole kilo so we use these numbers for planning. For ordering, most of us round. Some of us round up and some down. Either way, the over-run on the refuelling system will be about 60kgs. In flight, we'll round again and most of us round conservatively, or pessimistically if you like. It's always nice to know you have enough fuel. As for post flight, the exact number is used for fuel burn statistics. We'll also use the precise fuel density described in as many decimal points as supplied - apparently we pay less in "green tax" if we use the correct numbers. But it is important to consider that the aero engine manufacturer probably did their sums starting in pounds calculated from fuel flow units calibrated in gallons per hour. This was then converted it to kilos and used in an FMS system initially designed to work in pounds. The fuel density is normally "guessed" at 0.8 but it certainly varies between 0.794 to 0.804. The saying "Measured with a micrometer, marked with chalk and chopped with an axe" springs to mind.

But for navigation, I think most of us will enter our starting position as accurately as we possibly can. Small errors at the start of a flight build up to massive ones at the end.

As for conversions - we have a little "You Beaut" page in our FMS that converts pounds, gallons, kilos, litres etc. If it can find it. Failing that the Mk.I noddle or the electronic shoveler.

thanks for your reply