When conducting an RNAV approach do you need to adjust for temperature? How do you do this? If the temperature is higher than ISA you’d also be higher on the descent path than a standard day so how do you compensate for this?
Basically by looking out the window and aiming for the correct aim point.
Like some have said you can enter an average ISA deviation ( for the entire descent) into the FMC and it will move your TOD point a little bit, but don’t confuse this with the on slope indication as you cross the threshold. The only correction for above ISA conditions as you come down final is your eyeballs. You can see this any time you operate in high temperatures. You’ll get a sense visually that you are a bit high when showing on slope and that is because you are. The altimeter is under reading.
From a training guide;
The altimeter will under read in an above ISA atmosphere causing the aircraft to fly a slightly steeper approach. For example on an ISA +20 day the altimeter will under read by 4% for each 10 degrees above ISA, times the height above the airfield. This means that the aircraft will arrive at the 250' minima 20 feet high and at the threshold 4 feet high.
It’s nicer to disengage and fly for a visual aiming point earlier rather than later so that you have a smaller correction to make. If it’s really hot I’ll say ‘visual aiming point’ so that my colleague doesn’t wonder why I’m drifting a bit low on the vertical guidance. It’s quite small stuff most of the time so probably something to think about after you’ve been on the machine for a wee while and wanting to finesse things. With less experienced people you can clearly tell when they stop following the PFD and start aiming at the runway visually because they have to shove the nose down to pick up the correct point on the runway. This in turn makes it tricky for them because the last 20 seconds is less stable with more adjustments than if they had flown visually for the last 1000ft.