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Jsol

Glideslope callout

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Hi guys. This might be a noob or silly question. But how do you disable glidslope callout? Its really annoying when i land. I tend to glide the plane low and slow most of the times and im already accustomed to it. I just want to disable the callout. Anybody know how?

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Flying too low, taking off roofs and antennas and approach lights is not the way to fly any airliner.

 

When you hear that 50ft call out (that should accur over the threshold) that means your radio altimeter antenna is in 50ft.

Your landing gear is 20ft lower than that!

 

But anyway.......click the G/S inhibit switch just above the landing gear!

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Anybody know how?

 

Fly the airplane properly.  I mean that in the nicest, and most straightforward way.

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When you hear that 50ft call out (that should accur over the threshold) that means your radio altimeter antenna is in 50ft.
Your landing gear is 20ft lower than that!

The RA antenna is certainly higher than the wheels, but radio altitude is calibrated to read main wheel height above ground at a typical approach attitude. The "fifty" call is when wheels are 50' above ground. Whether it occurs at the threshold or not depends on where the glideslope antenna is located on the aircraft type concerned. If on the ILS, the g/s antenna will cross the threshold at 50', the main wheels will be lower than that, possibly the 20 feet you mention. On the 777 the g/s antennae position switches to the nose gear doors when the gear is down, which helps increase the threshold crossing height of the aircraft.

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If on the ILS, the g/s antenna will cross the threshold at 50', the main wheels will be lower than that, possibly the 20 feet you mention.

Since we were talking ILS, the figure on page 5.22 of the PMDG-777-FCTM applies.

And so, as you said antenna at 50ft.....gear at 30ft (depending on 777 type).

 

 

The RA antenna is certainly higher than the wheels, but radio altitude is calibrated to read main wheel height above ground at a typical approach attitude.

Yes, true.

 

The "fifty" call is when wheels are 50' above ground.

Yes, you got me there, my mistake.

Otherwise those "30", "20", "10" calls would occur after touchdown or never, lol.

 

But despite my mistake there, my point was ofcourse, that if you cross the threshold below glideslope.....your gear might get dangerously close to tarrain/obstacles before touchdown.

 

On the 777 the g/s antennae position switches to the nose gear doors when the gear is down, which helps increase the threshold crossing height of the aircraft.

Did not know that......looked everywhere.........where did you get that info from?

With 2 degrees pitch up.....would that not lower the main gear crossing height?

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On the 777 the g/s antennae position switches to the nose gear doors when the gear is down, which helps increase the threshold crossing height of the aircraft.

 

Along with Rob, I am not sure this is the case and would really like to have a reference. I've read that the B744 does have separate capture antenna in radome and track antenna on main wheel door; however, a thorough search through the FCOM and FCTM does not indicate that the B777 uses this approach. In fact, the text and diagram in FCTM pg 5.22 supports the notion that there is only one GS antenna and it is in the radome. Note that for the -300ER crossing threshold eyepoint at 58 ft the main gear is only 29 ft above runway.... adding to the argument that coming in below GS might not be good for your health.

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Did not know that......looked everywhere.........where did you get that info from?

With 2 degrees pitch up.....would that not lower the main gear crossing height?

 

If you put the glideslope antenna lower on the aircraft that will raise the position of the gear relative to the ILS and increase the gear height as the aircraft crosses the threshold.

 

 

Along with Rob, I am not sure this is the case and would really like to have a reference. I've read that the B744 does have separate capture antenna in radome and track antenna on main wheel door; however, a thorough search through the FCOM and FCTM does not indicate that the B777 uses this approach. In fact, the text and diagram in FCTM pg 5.22 supports the notion that there is only one GS antenna and it is in the radome. Note that for the -300ER crossing threshold eyepoint at 58 ft the main gear is only 29 ft above runway.... adding to the argument that coming in below GS might not be good for your health.

 

Here's the diagram I found on the net which shows antenna locations for the 777-200. I don't have a source for it but it looks like a typical Boeing drawing. The antenna switching with gear down is my assumption. That's how it works on the 747, so it makes sense they used similar switching logic on the 777.

 

777antennae.jpg

 

Pose #6 links relevant the Boeing patent application.

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That's how it works on the 747, so it makes sense they used similar switching logic on the 777.

 

The 742 has a GS antenna in the nose gear door, the 744 was in the main gear door.... it doesn't follow that they need to implement the same strategy in the 777 familty; however,  the FCTM reference could apply if the track antenna was in the nose gear door as inidicated above, which looks very plausible to me. Also, I found a reference to a warning annunciation in the event that two or more ILS receivers are using the wrong antenna, which also leads to the nose gear location plausibility. I can buy that logic, but again need to point out that the -300ER crossing threshold eyepoint at 58 ft the main gear is only 29 ft above runway.

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Ok, Kevin....you were correct!

 

I had to open up the short version mainenance manual I happen to have to get to the bottom of this, but it paid off!

 

The radome holds 3 Localizer antennas (Left,Center,Right) and 3 G/S antennas (L,C,R).

(The VOR antenna by the way is in the top of the vertical stabiliser)

Might sound stupid, but I had no idea those antennas were under the radome. I thought they would be somewhere along the belly (but anyway, it explains my previous question).

 

Further more, there are three so called Glide Slope TRACK antennas.

These are located on the leading edges of the two aft nose gear doors.

Left and Center G/S track antenna - on left aft nose gear door.

Right G/S track antenna - on the right aft nose gear door.

(maybe you guys can go look for them on the PMDG (I am not at home). They look pretty small in my documents and pictures)

 

All those localizer/glideslope/VOR signals go through switches and then to their respective multimode receiver (MMR). So we have 3 MMRs.

And those switches are told by their respective Left,Center,Right autoflight director computer (AFDC) which antenna should be used.

 

So you get:

Left loc antenna (radome) + left G/S antenna (radome) - through the switch - to Left MMR.

 

or, if the AFDC commands the G/S antenna switches to switch:

Left loc antenna (radome) + left G/S TRACK antenna - switch - Left MMR.

 

And ditto for the center and right system.

 

When the AFDC commands the switches to change to the G/S track antennas.....I do not know.

May be gear down (makes sence), but could also be later like 600ft AGL as this is the altitude prior to whitch multichannel approach mode must have been selected (Land 3 or 2 displayed) or an autoland becomes impossible.

 

But the G/S track antennas are definately used for the reasone you stated Kevin.

They supply final approach and landing glideslope signals. My maintenance manual literally states that the track antennas are in a position to minimize the vertical distance between the antenna flight path and the main landing gear!

 

Cool stuff......definately higher learning no? ;-)

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I can buy that logic, but again need to point out that the -300ER crossing threshold eyepoint at 58 ft the main gear is only 29 ft above runway.

I don't question that. But if the glideslope antennae didn't switch to the nose gear door the gear height at threshold crossing would be even lower.

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When the AFDC commands the switches to change to the G/S track antennas.....I do not know.

May be gear down (makes sence), but could also be later like 600ft AGL as this is the altitude prior to whitch multichannel approach mode must have been selected (Land 3 or 2 displayed) or an autoland becomes impossible.

 

That's possible, but if it happened that late in the approach you would surely notice the raw data pointer jump when the antenna switched. There would be an adjustment in pitch if the AP was engaged too. The thing is you don't see the raw data pointer jump. This can be explained by the fact that normal procedure is to extend the gear when G/S is alive. As the pointer is already moving you don't notice it jump a small amount when the switch occurs. At 5 nm the G/S beam is wide so a few feet difference in antenna height would be small in terms of dots deflection.

 

 

Cool stuff......definately higher learning no? ;-)

 

Cool indeed and to think I only researched this because you mentioned threshold crossing height in post #2. That reminded me of something a 747 Training Captain who told me about how low the 747 main gear was to the ground at threshold crossing height. To make sure my reply to you made sense, I wanted to estimate where the 777 gear should be relative to the ILS. So I needed to know where the 777 G/S antenna was. Googling that diagram was a stroke of luck and it reminded me of the 747 arrangement. From work I've done on simulators in the past I knew how important the simulating exact position of the antenna was to get things right for low visibility landing training. The same 747 Training Captain who told me about the gear height had also told me about the antenna switching. Hence the two things are linked in my memory.

 

Serendipity.

 

The 742 has a GS antenna in the nose gear door, the 744 was in the main gear door.... it doesn't follow that they need to implement the same strategy in the 777 familty

Are you sure about the 744? Putting it in the main gear door would make a very big difference to the landing "picture" 742 pilots would have to adjust to. Also there's this detailed post I found on pprune which implies it was more like the 742.

 

The ILS capture antennas are under the radome, centre antenna is placed above the weather radar antenna and the left/right dual antenna is below the weather radar antenna. The change over occurs when the landing gear is lowered. The left/right dual antenna is on the aft left nose wheel door and the centre on the right aft nose door.

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