Actually using FF to set a speed was common practice on the 737-200
Not just on the 732, but on a great number of 'classic' turbo-jet aircraft.
Strictly speaking the only true measure of thrust/ power on these aircraft is EPR ( N1 with Turbo Fans as the Fan contributes a large portion of thrust) however as we know EPR is not a static value, ie if you set an exact EPR, then change speed the indicated EPR will change (Dynamic-static pressure). These older aircraft did not have digitally enhanced/ corrected EPR instrumentation!!
In days gone by it was discovered that trainee's tended to spend a large amount of time fixated on the EPR gauges (or worse still the tiny N1% gauges on the 737) in order to set a reference power, with the consequence that their instrument scan broke down.
Provided an engine is functioning correctly a given Thrust lever angle/ position will correspond to a given Fuel Flow, which in turn will give a steady EPR at a given speed & attitude. The end product of all of this was that if you set an accurate pitch and an accurate Fuel Flow the rest (speed/ EPR) will all settle down nicely. Thus setting power using Fuel Flow came about.
It helped of course that the Fuel Flow gauges were reasonable large too!
Not necessary on modern types, and of course not even possible as ECAMs and EICAS's dont display secondary engine information unless a problem exists (or it is selected...)
I should stress that FF was used to set power flying in the circuit/ training area and on approach. Take Off power was of course set reference to EPR (with an N1 cross check after Air Florida 'v' the Potomac).
To back up previous posters I recall the following working very well on the 737-200:
Level, 210kts, Clean, Pitch 6°, 1100FF per eng, (2200FF with an eng inop.)
Level, 250kts, Clean, Pitch 4°, 1250FF per eng, (2500FF with an eng inop.)
Level, 170Kts, Flap 5, Pitch 7°, 1300FF per eng,(2600FF with an eng inop.)
Level, 150Kts, Flap 15, Gear Down, Pitch 7°, 1600FF per eng (3000 eng inop).
3° G/S, Vref30+5kts, Flap 30, Gear Down, Pitch 1°, 1400FF per eng (or with Flap 15, Vref15+5kts and an eng inop, FF 1700)
Enjoy
