500 above
As the standard DR400 has no fuel flow indication the only way to accurately check the rate of fuel burn is to check how long it has taken to burn a known quantity of fuel.
With three or four fuel tanks (depending on the aircraft options) and a low level indicator that accurately indicates the remaining fuel in each tank this gives several "hard points" at which the fuel flow can be determined for the prevailing conditions on that particular flight.
I find it difficult to understand why you warn that this methode of determining the fuel state and remaining endurance of the aircraft is advice that one should be wary of.
Last edited by A and C; 24th Dec 2012 at 23:24.