LLZ and Glideslope Capture
 

Can any Boeing drivers comment on weather it is possible to capture the glideslope before the Localizer?

Imagine you are conducting a continuous descent in VS with APR armed and you slowly pass through the glideslope from above (not ideal I know). Will glideslope green annunciate on the FMA if the localizer has not already been captured, or is it normal to select LOC on the MCP if it is thought that glideslope capture might occur first?

Yes
 

757/767
1. Yes
2. Also yes
3. Yes again.

B 747 200 autopilot has VOR/LOC switch position and the next position is ILS if you switch it straight over to ILS before having captured the Localizer it will capture the glideslop and will announce on FMA.

With the switch selected in VOR/LOC the aeroplane will turn on the heading knob until it does capture the localizer, only once the LOC capture has announced do we(our company SOP) select ILS.

In the UK, I believe it's specifically prohibited to use GP info prior to LLZ capture. Pity MLS never caught on.

Ditto 737 & A320

Correct.

From an incident report....

"According to Boeing, the B737NG auto-flight system can be configured in two ways prior to aircraft delivery. In this respect, xxxx Airlines had the option to configure their aircraft’s auto-flight system to either inhibit glideslope capture prior to localiser capture or, as was the case with all of the xxxx Airlines B737 fleet, enable glideslope capture prior to localiser capture.

The option of enabling glideslope capture prior to localiser capture was recommended by Boeing for those operators trying to achieve fleet commonality and for those operating in terminal areas where FMC positioning can be relied upon."

So perhaps it is an option on all newer Boeing types.

The B737 Classic and the NG it is a customer option, pin selectable for GS capture or GS inhibit prior to LOC capture.

As already said above, then yes Boeing aircrafts can be configured in such a way with the pin selection that they can capture the GS first. Why anybody would want that I do not understand, but it is an option.

Apparently the same is possible for airbii. Both on our 737s and A320 there will be no GS capture before LOC capture.

737-200 sim exercise years ago .. crew caught a false LLZ off an arc and then the GS... took a while for them to work out what was going on.

Emphasises the benefit of positively tracking over the LOC or whatever fix defines the gate or, at the very least, using something else to check that you are where you might like to think you would like to be ...

BOEING
Flight Crew Training Manual
Flight Operations REVIEW
A MESSAGE TO FLIGHT CREWS FROM THE BOEING COMMERCIAL AIRPLANE GROUP
Aircraft Applicability: 737, 747, 757, 767, 777
Reference Number: 737-29, 747-29, 757-25, 767-25, 777-02

Options are available on all Boeing aircraft to inhibit early glideslope capture. Glideslope deviation and localiser deviation indications are always available on both pilot's flight displays for all FCC options.

Whether EFIS-equipped or not, there may be legitimate and valid reasons for an early glideslope capture capability to cope with ATC altitude clearances. Its use is safe and effective provided proper situational awareness is employed in the decision to exercise early glideslope capture. Specific situational awareness should be part of any decision to intentionally capture glideslope early. Pilots should be aware of the inherent risks associated with performing early glideslope capture if not properly aligned on the localiser course.

That's like a NOTAM I saw recently about the runway center line lights being on test, do not use. I tried to turn a blind eye.

The GP info is very useful for descent planning sometimes. But that doesn't mean you descend with it below a cleared altitude or established on the LOC first. Any pilot knows that. So I've always found those remarks on the approach plates a bit silly that GP info cannot be used for reference before established on LOC.

The reason for that is that often there is a false GS. I don't recall the maths involved but is often at twice the GP angle. Someone with a flight check background would be able to have the definitive answer.

I have flown one aircraft that unbeknownst to me (lease aircraft) could capture GP without the LOC. The pitch down rate for the false GP was truly impressive!

I've heard quite often from ATCOs the nice phrase "descend with the glide" when they noticed that their vector didn't allow to intercept the LOC first. In that situation a capture GP first feature would have helped, but alas it is not a big issue without it either.