B7378 tips?

[Occy]

I’m not a massive fan of spending too much time heads down in “the box” at low level, as some people here mention. However, if the missed approach is complex, it’s worth making sure you at least tidy up the legs page so the waypoints sequence and you don’t lose LNAV guidance for the missed approach.

[Paulm1949]

Thanks for the replies.

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?

[Banana Joe]

In the FORECAST page that you can access from the DESCENT page, you enter the ISA deviation and QNH. I fill this page for every descent and approach.
The upcoming FMC update will also bring in further improvements but these are an option.

[Paulm1949]

Is that ISA deviation for the whole descent or for the destination field ?

[Banana Joe]

Whole descent. If you don't update it when there's a high pressure at the Transition Level you will find yourself high. With a high QNH in the forecast page, the FMC recalculates and moves the TD a few miles before.

VNAV is a good system that works well if the information it is given is correct. It's trash in, trash out.

[Paulm1949]

Yes but what about the temperature?

[Banana Joe]

Sorry, I confused the two. But it's exactly the same.
You insert the ISA deviation at destination airfield to cater for it.

[FlyingStone]

Originally Posted by Banana Joe

You insert the ISA deviation at destination airfield to cater for it.

It should actually be average ISA deviation during descent, but very few OFPs provide such data. In practice, inserting ISA deviation rarely makes a big difference to the calculated descent profile.

[Banana Joe]

That's true.
Taking the values at the 3 altitudes whose descent winds are inserted in the FORECAST page and interpolate a rough average between them would not be wrong in my opinion. But that's too much into details maybe.


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[73qanda]

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.

[Paulm1949]

In this day and age, could it not fly 2 reds/2 whites perfectly whilst in LNAV/VNAV? After all its a GPS derived signal.

Any hard earned tips guys with the fms in particular?

[FlyingStone]

In this day and age, could it not fly 2 reds/2 whites perfectly whilst in LNAV/VNAV? After all its a GPS derived signal.

VNAV profile uses barometric altimeter, which has its usual failings when outside temperature does not conform to ISA. GPS for vertical profile is only used for SBAS (LPV), which is not yet available on the 737 to the best of my knowledge.

ICAO does not prescribe any procedures for correcting the altitudes for temperatures warmer than ISA, and one is not to fly below the prescribed altitudes by the State, hence you will be high on profile in hot weather and will have to deal with it once you are visual, as in any other aircraft.

[Banana Joe]

LPV is available as an option and I know of an operator whose Classics and NGs are being retrofitted and with simulator training scheduled.

[73qanda]

In this day and age, could it not fly 2 reds/2 whites perfectly whilst in LNAV/VNAV?

Not on an ISA+ day.
You are high by 4% of your height above the airfield for each ISA +10 degrees.
It doesn’t sound like much but it is useful to be aware that it’s going to happen. Particularly if the heat is going to cause up draughts etc as you fly over the concrete, sometimes it all adds up to a flare you’d rather forget As usual though, the answer is to look out the window and make the picture right.

[Uplinker]

Originally Posted by 73qanda

Basically by looking out the window and aiming for the correct aim point.........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.

...assuming you are not IMC until just above minimums.......

[Wallace737]

For RNP approaches you can use LNAV/VNAV and it'll do a grand job, temperature permitting.

If the approach is to LNAV/VNAV minima, no cold temperature correction is required providing it isn't below the minimum approved temperature (this will be promulaged on the approach plate)

If the approach is to LNAV only minima you can use LNAV/VNAV but must temperature correct all altitudes below the temperature corrected MSA if OAT at aerodrome is 0 degrees C or less.

Of course operator must have approval, aircraft with GPS and both crew PBN endorsed on licence

[Paulm1949]

So you could be coming out of IMC at DA and seeing 3 whites.

Any tips guys that you’ve learnt along the way would be highly appreciated!

[Banana Joe]

Trim, a lot.
​​​​​​With any jet, don't pump or cycle the rudder pedals with one engine inoperative and don't get slow or she will bite you very hard. For most engine out scenarios, 4.5 units of rudder trim is just perfect.

For the rest, it's a big Seneca.

[Paulm1949]

Thanks. Any good tips with the fms, apart from what’s been discussed ?

[Wallace737]

Originally Posted by Paulm1949

Thanks. Any good tips with the fms, apart from what’s been discussed ?

Yeah, it isn't the priority. Fly the plane first. When it's doing what you want it to do, then tidy up the FMC