Boeing Lounge 737 radalt and FD/AP

Roger Roger

Roger Roger

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had an interesting one the other day and I’d like to see what the Guppy brain trust has to say about it. My leg to fly, climbing out of the Midwest in the 20s or so the other day, my radalt starts flickering between normal (not showing), 1500-2000’, and a yellow “RA”annunciation where the radalt readout would be. After a minute or so it stopped and acted normal. 3 hours later on approach, still no more apparent issues with my radalt, after intercepting final in LNAV I hit the button to switch to LOC and my lateral FD bar disappeared. AP stayed engaged and lateral mode FMA showed LOC. Then approaching GS intercept, I hit APP, GS captured, and then the vertical FD bar disappeared and the AP disconnected. I went to hand flying and my CA wasn’t able to restore either my FD or my AP. Reading in the systems handbook after, a faulty radalt will cause the FD to bias out of view once you’re in LOC capture mode so I’m fairly sure that’s what happened. First, does this seem correct? What I’m a bit surprised about is that 1. The radalt would stay failed/faulted with no annunciation and 2. That none of the manuals I could find (QRH, systems handbook, flight handbook) gave a procedure or list of things effected with an inop radalt, which might have been nice to have a heads up on. I guess it’s just one of those bits of trivia you have to know.
 
Roger Roger said:
had an interesting one the other day and I’d like to see what the Guppy brain trust has to say about it. My leg to fly, climbing out of the Midwest in the 20s or so the other day, my radalt starts flickering between normal (not showing), 1500-2000’, and a yellow “RA”annunciation where the radalt readout would be. After a minute or so it stopped and acted normal. 3 hours later on approach, still no more apparent issues with my radalt, after intercepting final in LNAV I hit the button to switch to LOC and my lateral FD bar disappeared. AP stayed engaged and lateral mode FMA showed LOC. Then approaching GS intercept, I hit APP, GS captured, and then the vertical FD bar disappeared and the AP disconnected. I went to hand flying and my CA wasn’t able to restore either my FD or my AP. Reading in the systems handbook after, a faulty radalt will cause the FD to bias out of view once you’re in LOC capture mode so I’m fairly sure that’s what happened. First, does this seem correct? What I’m a bit surprised about is that 1. The radalt would stay failed/faulted with no annunciation and 2. That none of the manuals I could find (QRH, systems handbook, flight handbook) gave a procedure or list of things effected with an inop radalt, which might have been nice to have a heads up on. I guess it’s just one of those bits of trivia you have to know.
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Most certainly not a Guppy Puppy (although I see a future where I get forced to one) but it's not uncommon on OtherBrand(tm) to have a radar altimeter pick up a plane flying underneath you for a second or two. Wouldn't be an issue still 2 hours later though.
 
The radio altimeter wipes out a bunch of stuff when it goes. During upgrade they dug into that during MEL training. I don’t have my iPad handy right now to look but I remember that it really degrades the airplane.
 
BobDDuck said:
Most certainly not a Guppy Puppy (although I see a future where I get forced to one) but it's not uncommon on OtherBrand(tm) to have a radar altimeter pick up a plane flying underneath you for a second or two. Wouldn't be an issue still 2 hours later though.
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That’s what I thought, so I turned the TCAS to down and zoomed in and had no one there (made a crack about the military, not sure if the ca found it funny). Shouldn’t show an RA fail flag though right?
 
arkflyr said:
The radio altimeter wipes out a bunch of stuff when it goes. During upgrade they dug into that during MEL training. I don’t have my iPad handy right now to look but I remember that it really degrades the airplane.
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I didn’t think to look at the consequences in the MEL, that’s a good resource for sure. Thanks!
 
Our QRH has limits on approaches with an Radio Alt failure though it doesn't go into too much detail other than which A/P to use depending on which RA failed and the effects on ILS/IAN capture with notes about preferring RNAV (GPS) or VOR approaches in LNAV/VNAV.

Curiously I found spurious Radio Alt fails were fairly common for me in the old Canadian Space Shuttle. Certain planes would do a fantastic job of collecting oil/fuel/hydraulic/black airplane goo on them which would mess them up. Usually only an issue in winter when snow and much was added to the mix of what was thrown upon them, but I remember a couple birds in particular it was basically necessary after every leg to go out and wipe them off to prevent issues.
 
Just another reason The Guppy Sucks™
Had the FOs RA MEL'd (holy acronyms) a few weeks ago and it did indeed make their FD do funky things.
Have you had a Max HSI wabble after landing and while holding in position yet? Real solid piece of kit...
 
Karnage said:
Our QRH has limits on approaches with an Radio Alt failure though it doesn't go into too much detail other than which A/P to use depending on which RA failed and the effects on ILS/IAN capture with notes about preferring RNAV (GPS) or VOR approaches in LNAV/VNAV.
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See, I was kind of expecting our QRH to have something about it but it hardly mentions the RA at all, and never in the context of having one quit in flight. It does show you where the circuit breaker is though.
Karnage said:
Curiously I found spurious Radio Alt fails were fairly common for me in the old Canadian Space Shuttle. Certain planes would do a fantastic job of collecting oil/fuel/hydraulic/black airplane goo on them which would mess them up. Usually only an issue in winter when snow and much was added to the mix of what was thrown upon them, but I remember a couple birds in particular it was basically necessary after every leg to go out and wipe them off to prevent issues.
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On the few Caravans I worked on that had them I remember corrosion being a real big thing
Skåning said:
Just another reason The Guppy Sucks™
Had the FOs RA MEL'd (holy acronyms) a few weeks ago and it did indeed make their FD do funky things.
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Yeah, looking at the MEL even the FOs side does some fun stuff and it looks like you straight up can’t defer the CA side. Good bit of info to put in the back pocket for future.
Skåning said:
Have you had a Max HSI wabble after landing and while holding in position yet? Real solid piece of kit...
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Not that I’ve noticed…do elaborate
 
Roger Roger said:
Not that I’ve noticed…do elaborate
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Some "known" software? thing where when you hold position after landing for longer than a certain time, the compass thingys on the screens start gyrating back and forth quickly. Like this, but faster:

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I still remember the first time I was told to do a mask test on a radalt system on the mighty COD. I thought I was being hazed..

“You want me to take a trash can lid and hold it up to the forward antenna? Sure right after I grab a gallon of prop wash and fill out my ID10-T form..”

Twenty minutes later there I was, masking the radalt with a garbage can lid..

For the 737, I know radalt issues can throw off any auto land capability(obviously) but messing with loc guidance is weird, as that’s not really related in any reception, carriage and display of data afaik. Thanks for sharing that one! Did you guys try Autopilot A afterwards? Or was the guidance out to lunch by then giving you invalid info onside?

I’ve been pleasantly surprised with the old school Honda Civic or Toyota Corolla vibe of the 737. Out of all my type ratings, this thing has had me in the QRH a fraction of the time as others. Great, now that I said that I’m sure I’ll have a doozy pop up this next four day.
 
JDean3204 said:
For the 737, I know radalt issues can throw off any auto land capability(obviously) but messing with loc guidance is weird, as that’s not really related in any reception, carriage and display of data afaik. Thanks for sharing that one! Did you guys try Autopilot A afterwards? Or was the guidance out to lunch by then giving you invalid info onside?
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We didn’t but CA had his FD the whole time so I bet AP A would have engaged. It’s pretty clear from reading the MEL that losing a radalt messes with something in the approach mode logic which is why if it senses a failure/fault it just pulls the FD as soon as you switch to LOC capture. I’m still curious that the RA would fail/fault and maybe, maybe not give you a flag though.
JDean3204 said:
I’ve been pleasantly surprised with the old school Honda Civic or Toyota Corolla vibe of the 737. Out of all my type ratings, this thing has had me in the QRH a fraction of the time as others. Great, now that I said that I’m sure I’ll have a doozy pop up this next four day.
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It’s the most reliable airplane I’ve flown, probably partly because it’s so dumb… the airplane doesn’t realize you have a problem until something breaks hard. Hell, apparently you can have a whole pack not working and the airplane won’t let you know.
 
BobDDuck said:
Most certainly not a Guppy Puppy (although I see a future where I get forced to one) but it's not uncommon on OtherBrand(tm) to have a radar altimeter pick up a plane flying underneath you for a second or two. Wouldn't be an issue still 2 hours later though.
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Aircraft order announcement today sure seems to indicate as much.
 
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