How to do a successful go-around
Performing a successful go-around is a straight forward procedure on the 747 and is performed in the same manner whether an instrument or visual approach (balked landing) is flown. The Go-around procedure can be flown manually via the Flight Director (FD) or automatically via the engaged autopilot. The Go-around is armed and the reference thrust changes to GA when the flaps are out of UP or the glideslope (GS) is captured.
Pressing the TO/GA switch (or the screw next to the autothrottle arm switch) will activate the Go-around mode. this mode will remain active even if the aircraft touches the ground during the GA maneuver. If the FD's happened to be switched off then they will automatically reappear when TO/GA is selected.
What happens when the TO/GA switch is depressed?
With the first push of the switch:
- Roll and pitch modes activate in TO/GA and this appears on the Flight mode annunciator (FMA) at the top of the nav display (ND)
- Autothrottle activates in thrust (THR) to establish an approximate 2000 FPM climb.
- The TO/GA pitch mode initially commands a go-around attitude and then transitions to speed as the rate of climb starts to increase. This speed will normally be between the commanded speed set on the IAS MCP window, and commanded speed plus 25 kts.
- The TO/GA roll mode will command either existing ground track or selected heading (whichever option you have selected in PMDG>options>AFDS>TO/GA Roll mode in the simulation.)
With a second press of the TO/GA switch:
- Autothrottle will now command full Go-around thrust and the thrust reference will change to THR REF.
What happens next?
The aircraft will happily climb away without you doing anything. It will not follow the missed approach course though as is it just maintaining the last ground track or selected heading (whichever option you selected). You would of course reconfigure the flaps and gear but we will look at this later. So here we are climbing away up towards our missed approach altitude which we had diligently set in the MCP altitude window as we were flying down the captured GS. Assuming we do not select any other roll or pitch mode the aircraft will still be climbing with the roll and pitch modes both showing TO/GA on the FMA.
At level off altitude:
- The pitch mode will change to altitude hold (ALT). If we had conducted an autopilot ILS approach and go-around all autopilots, except the first autopilot that was initially engaged, will disengage.
- The A/T remains in THR or THR REF until a SPD mode is selected. The speed will increase to within 5 kts of the current flap settings placard speed or the gear extended limiting speed.
- TO/GA will remain the active roll mode until another mode is selected.
So how do I get out of this TO/GA mode?
It is a little bit tricky and there is a trap to be aware of.
- Below 400 ft Radio alt you will need to disengage the autopilot and turn off BOTH FD's.
- Above 400ft Radio Alt select a different roll and or pitch mode. At this point all A/Ps except the initial one in command will disengage.
So what is the trap?
If you had flown the ILS approach with the AP engaged in an asymmetric condition (1 or more engines out on the same side) when you reached 1500ft AGL on the approach the other 2 A/P's would have engaged as well to give you 3 A/P's controlling the aircraft (This gives the necessary A/P redundancy to conduct Cat 2 and 3 landings. The rudder will be taken care of by the 3 A/Ps. When you select another roll mode above 400ft AGL on the go-around, 2 of the A/P's will drop out and the rudder will return to the trimmed position before the 3 A/Ps engaged on the approach. There is a lot more asymmetric power produced now on the go-around and the aircraft will want to suddenly yaw and roll towards the failed engine(s). This can be a real surprise if you are not ready for it! You have been warned!
So run me through the whole procedure from the time I elect to go-around
Let's assume we are doing an ILS approach and the A/P is engaged. First of all before doing the approach, on the LEGS page, try to enter a speed beside the missed approach waypoint altitude (some missed approach waypoints will not take a speed as it depends on how the waypoint is coded). If you can try entering 200 kts ie. 200/3000. When you go around and eventually select VNAV it should aim for this speed. The PMDG model sometimes does not take notice of this so be warned.
Here we go:
- Press the TO/GA switch (or screw beside the A/T arm switch. Verify the aircraft starts to pitch up and power is being applied.
- Select Flaps to 20
- Positive climb select GEAR UP. Be aware that approximately 40 ft of altitude will be lost during the GA procedure. If done at a low level it is possible to touch down during the maneuver. The GA will still be commanded and it will lift off.
- Normally the Pilot not flying (PM)(in this case the FO) would ensure that the FMA's were indicating THR or THR REF and TO/GA TO/GA on the roll and pitch modes respectively. As we don't have an F/O now is a good time for you to check this for yourself.
- 400ft AGL select another roll mode (normally LNAV if you have the missed approach procedure showing on the legs page).If you are asymmetric then be prepared for the swing and roll toward the failed engine(s) and use rudder to keep straight/ wings level. Trim the rudder asap. Make sure the FMA shows the new roll mode i.e. LNAV and not TO/GA.
- at 1000ft AGL select VNAV. Ensure the FMA shows VNAV and not TO/GA.
- retract the flaps on schedule as per a normal departure. I recommend that you initially only retract the flaps to 5. Watch the speed bug and make sure it stops at 200 kts. If it goes past it then open the MCP IAS speed window and set 200 kts. This is now a nice comfortable position to be in. You are at a suitable speed that you can enter the holding pattern, if required, and know that you wont break any holding speed requirements. It is also a good time to gather your thoughts as to what your next course of action might be....divert or get vectors for another go or try a different runway.
From here on you can continue on as per a normal flight.
For a manually flown approach do exactly as described above except when you press the TO/GA switch smoothly raise the nose to 15 degrees nose up initially. Then follow the FD commands.
Note: I have observed in the PMDG simulation that when the TO/GA switch is pressed only once that the speed can decay to a dangerously low level. If this looks like it is about to happen then press the switch again to get full go-around thrust.