View Full Version : A319/320 fly up to glideslope
CaptainMongo
21st Dec 2019, 13:00
A319/320 fleet. We had a few of these reports at our outfit. (I don’t have access to the complete reports, only the anomaly described.)
Below the glide slope, in ALT, after arming APPR the aircraft leaves the altitude and climbs up to capture the glide slope.
Has anyone experienced this?
turbidus
21st Dec 2019, 13:45
https://www.pprune.org/tech-log/618546-airbus-a320-final-app-mode.html
OPEN DES
21st Dec 2019, 14:58
Hi,
Same as the poster above I am suspecting the context is a 3D NPA where FINAL APP would be the guidance mode used through the APPR p/b.
in some cases where there is no level segment coded prior to the FDP the descent profile is propagated up outwards from the FDP. But there will be a level acceleration segment calculated to reduce from the typical 250: i.e. there is a level segment after the DECEL pseudowaypoint equivalent. Typically this is round about the 15NM mark assuming a decelerated app. When pushing the APPR p/b early you could find yourself inadvertently capturing the level
segment albeit already reduced from 250. The altitude of the level segment is variable and typically between 3000 to 4000 aal. When you satisfy the engagement condition of -150ft you could see FINAL APP engaging and the a/c climbing and possibly even leaving ALT...
sorry for the quick write-up..
brgds
CaptainMongo
21st Dec 2019, 18:09
It’s an informative video, but it doesn’t specifically address my question. The first few minutes of the video apply to an ILS approach, ie don’t arm LOC if the approach routing will take you across the ILS course. The remainder of the video applies to non-ILS APPR.
The instances I am referring to occurred when flying an ILS approach. The aircraft was in level flight below the glideslope. After arming APPR, the aircraft left altitude and climbed to capture the ILS glideslope.
Fursty Ferret
22nd Dec 2019, 02:47
I'm aware of issues where the aircraft will climb to capture a false glideslope, but in these cases the false lobe crossed the aircraft level, leading to GS* followed by an abrupt pitch up and entry into alpha protection.
I've never seen it climb to capture a "normal" glideslope.
It has happened to me, just once, in an airframe that I have been flying regularly for years and in an airport where I have been landing for years as well. So no idea why in that specific time and place the airplane decided to leave altitude and climb more than 250' to capture the G/S.
Citation2
22nd Dec 2019, 18:51
worth reading : https://www.onderzoeksraad.nl/nl/page/6819/dangerous-autopilot-response-due-to-false-glide-slope
turbidus
23rd Dec 2019, 09:57
It has happened to me, just once, in an airframe that I have been flying regularly for years and in an airport where I have been landing for years as well. So no idea why in that specific time and place the airplane decided to leave altitude and climb more than 250' to capture the G/S.
250' below GS??
CaptainMongo
23rd Dec 2019, 16:12
“worth reading : https://www.onderzoeksraad.nl/nl/pag...se-glide-slope (https://www.onderzoeksraad.nl/nl/page/6819/dangerous-autopilot-response-due-to-false-glide-slope)”
Yes excellent, I believe that report is based on this one:
Pitch-up Upsets due to ILS False Glide Slope
The Hague, June 2014
The reports issued by the Dutch Safety Board are open to the public. All reports are also available on the Safety Board's website www.safetyboard.nl (https://www.pprune.org/www.safetyboard.nl)
FalconFan
23rd Dec 2019, 23:20
250' below GS??
I assume when about a NM outside the FAF.
FlightDetent
23rd Dec 2019, 23:39
I've seen something similar, but not from ALT. -V/S, changed to GS* way too early and started climbing.
If you can say that again, did it fly up away from the FD bars that were commanding level flight with ALT engaged?
It did happen quite quickly so I can't say if the pitch flew away from the FD bars and then the FD changed to G/S* or if the FD mode changed by itself to V/S to climb towards the G/S.
I strongly suspect it was the first case though. Maybe the APPR mode captured the G/S too far away and commanded the airplane to leave the present pitch attitude disregarding the FD bars. What I can clearly recall - other than the usual "WTF!" - was the altitude alarm which, if my memory doesn't fail me, gets trigger when the airplane drifts away 250' or more from the altitude maintained.
Bright side: it woke me up in time for the landing!
FlightDetent
24th Dec 2019, 09:57
Mine were A319s with a Honeywell box, cannot recall how close or far from the threshold. Being a CDA freak, I would use -V/S all the time. A pronounced, uncommanded positive climb up to lock the GP is something that rings a very distant bell but was weird enough for the brain to store it. Too vague to describe and discuss with colleagues, too infrequent to nail what it was, just a memory of being upset with the machine. Definitely not the F2 balloon effect, which one'd use deliberately if in need for something similar.
Perhaps we need to redefine the scales?
Look, what is it doing?
Look, it's doing it again.
Do not make it do that again.
I wished it stopped doing this.
-------
Merry Christmas everyone.
sonicbum
24th Dec 2019, 12:11
A319/320 fleet. We had a few of these reports at our outfit. (I don’t have access to the complete reports, only the anomaly described.)
Below the glide slope, in ALT, after arming APPR the aircraft leaves the altitude and climbs up to capture the glide slope.
Has anyone experienced this?
From the FCOM SOP
ICAO defines the envelope where the quality of the G/S signal ensures a normal capture. This envelope is within 10 NM, ±8° of the centerline of the ILS glide path and up to 1.75 θ and down to 0.3 θ (θ = nominal glide path angle).
When arming the approach well outside of the normal G/S capture envelope, a spurious G/S* engagement may occur due to a wrong G/S deviation signal.
Whenever the pilot notices the pitch movement, or the spurious G/S*, or the trajectory deviation, the pilot will immediately disconnect the AP, if engaged, to re-establish a normal attitude and will disengage APPR mode.
CaptainMongo
25th Dec 2019, 23:15
From the FCOM SOP
ICAO defines the envelope where the quality of the G/S signal ensures a normal capture. This envelope is within 10 NM, ±8° of the centerline of the ILS glide path and up to 1.75 θ and down to 0.3 θ (θ = nominal glide path angle).
When arming the approach well outside of the normal G/S capture envelope, a spurious G/S* engagement may occur due to a wrong G/S deviation signal.
Whenever the pilot notices the pitch movement, or the spurious G/S*, or the trajectory deviation, the pilot will immediately disconnect the AP, if engaged, to re-establish a normal attitude and will disengage APPR mode.
Are you really 100 years old? :)
Thats good stuff. I oftentimes wish we used the manufactures FCOM, but we don’t and never will. It’s just the way my company is.
I’ll use that in an article I’m writing. Thanks and Merry Christmas, old man...
sonicbum
26th Dec 2019, 11:54
Are you really 100 years old? :)
Nah... ;-)
Thats good stuff. I oftentimes wish we used the manufactures FCOM, but we don’t and never will. It’s just the way my company is.
I’ll use that in an article I’m writing. Thanks and Merry Christmas, old man...
Merry Christmas !