FMC and go-arounds
 

With modern FMCs seemingly capable of all sorts of tricks, I was wondering...

Are any missed approach procedures loaded into the FMC as part of the flight plan? In other words, can a missed approach procedure be performed by the auto-pilot in 'managed' mode? Obviously there would have to be a trigger...maybe the pilot selecting TOGA?

At least for our database set on the 737 we have the missed approach procedure in the database for every instrument approach we can select. So just continue flying past the runway point it will continue to fly the missed approach, since most end in a holding pattern it will join the hold and fly that until it flames out. Exactly as it happened in the Helios case.

On the 757 go-arounds are as described in the previous post. G/A mode is armed whenever Approach is armed or the flaps are down, then if you want to go around at any time, press the go around switches on the throttles and away it goes.

You have to remember to select LNAV though for it to fly the lateral track as LNAV is not normally used for approaches. If you don't the aircraft will just track straight ahead. This can be at any time after 400ft AGL. Then at some point you'll want to reduce to climb thrust and increase speed, else the G/A will be flown at the speed you at which you commenced the go around. At 1000ft AGL we select Vref +80 kts (about 200kt) and Climb thrust. VNAV can also be used if you have selected a target speed and alltitude on the FMC.

Cheers

B744 very similar - press TOGA to go-around, then LNAV at 400ft agl and VNAV at 1000ft agl. Go-around tracks and altitude restraints should be in the FMC legs (and checked as part of descent/approach briefing). Currently there is no "go-around" button that will automatically fly the procedure to conclusion.

OK then, what's the THR button for?

From the 744 ops manual;

Thrust (THR) Switch
Operative from 400 feet after takeoff until landing; used to select climb thrust after takeoff or go-around.
Push –
Light remains extinguished (thrust limit function)
• after takeoff with VNAV or FLCH selected, changes reference thrust limit to armed climb thrust limit, or CON if engine inoperative
• after go-around, changes reference thrust limit to CLB, or CON if engine inoperative or CON selected
Note: Reference thrust limit remains GA when flaps in landing position or pitch mode is G/S.
Light illuminates (A/T mode function) - Changes A/T mode to THR REF when:
• reference thrust limit is CLB, CLB1, CLB2, CRZ, or CON and pitch mode is ALT or V/S
• reference thrust limit is GA and pitch mode is G/S or FLARE, or pitch mode is ALT or V/S and flaps in landing position


Got all that?:E

...and given all that, I never used it in 7 years on the 744!

777 update now automatically engages LNAV for missed approach track after selecting G/A.

Damn THR switch does different things at different times! Never understood it. Just learnt by heart when to press it during stressful times! As far as I could see, it 'bumped' the power setting to the next setting, sometimes. When one of the cabin crew once brought a visitor up, a young boy, they primed him to point up and say 'what does that button with T-H-R on it do?' He was nearly strangled.

Airbus remains in GA TRACK until the heading selector is oushed, thus engaging the NAV modes.

I never could find someone who could adequately explain that THR button. Safe to say I never used it on all my time on the 744.