Strange Autopilot Behaviour 737
Thread Starter
Join Date: Feb 2007
Location: Vancouver
Posts: 40
Likes: 0
Received 0 Likes
on
0 Posts
Strange Autopilot Behaviour 737
A few days ago, just after reaching cruise level 340 with VNAV/LNAV engaged an interesting "feature" appeared. Another aircraft was just passing us at level 360 and slowly overtaking. Autopilot was supposed to intercept next waypoint by making only a slight turn to the right. However, i felt a mild bump and the autopilot CMD reverted to CWS and started rolling to the left at a slightly higher rate than expected from "regular" LNAV turn. I watched the aircraft and it did not make an attempt to stop rolling, passing already 25 deg bankangle. I corrected manually and reengaged the autopilot. First attempt was HDG mode. Interestingly the aircraft tried to hold HDG while banking 20 deg. Basically flying sideways. In between i disengaged AP again and started to search for a trim problem, also having wake turbulence from overpassing aircraft in mind. LNAV again and aircraft starts banking to the left while trying to fly level. This continued for another 10 minutes and then everything was back to normal. I could not find any trim abnormalities or balance problems. The aircraft above was at this time already well ahead and i still suspect some wake turbulence. But why did the autopilot revert by passing thru this very mild jolt and the aircraft was not able to fly level without banking 20 degrees to the left for 10 minutes?
Any inputs greatly appreciated!
Cheers, hb
Any inputs greatly appreciated!
Cheers, hb
Psychophysiological entity
The overflying aircraft was probably a red-herring, but just supposing it was not. Just supposing something emanating from above could fool your systems!!
If this were the case, I think that it's such a serious anomaly that it should be investigated by the manufacturers.
If this were the case, I think that it's such a serious anomaly that it should be investigated by the manufacturers.
Join Date: Nov 2001
Location: S51 30 W060 10.
Posts: 197
Likes: 0
Received 0 Likes
on
0 Posts
once not long ago one of our captains reported an MCP failure..
it was weird, all of the sudden the whole thing blacked out...no course selection, no altitude window, anything....don´t recall what the fma said but that by itself is a pretty weird failure...they disconnected and flew the ils with the indications at the EADI...has anyone experienced this before?
btw cbs all in, no elec smoke or fire...
Saludos,
Sw.
it was weird, all of the sudden the whole thing blacked out...no course selection, no altitude window, anything....don´t recall what the fma said but that by itself is a pretty weird failure...they disconnected and flew the ils with the indications at the EADI...has anyone experienced this before?
btw cbs all in, no elec smoke or fire...
Saludos,
Sw.
Join Date: Aug 2001
Location: Europe-the sunshine side
Posts: 755
Likes: 0
Received 0 Likes
on
0 Posts
MCP failure, yes it may happen.
I've just seen on N.Geografic the accidents with the 737 rudder. The first accident and the incident happend like you said ,the 737 crossed some wake turbulance ,a jolt ,and the plane banked to left or right.
In the third case they were high ,and they had chance. Also ,the problem dissapeard by itself.
So, is the RSEP installed on your plane? This kind of occurence should be reported to aircraft manufacturer ,it may prove very important.
I can give you one example,happened 2 month ago ,big company,west europe.
" During flight control checks,a slight diff in pressure was felt on left ruddr.Then a kick was felt as the rudder was centerred and the Stby rudder light illuminated.After removing panels from the fin it was found that the rudder has not been modified to reflect the aircraft modification state "
Amazing ,right ?.
So ,make sure you report that to tech department,chief pilot,etc...be sure they found what was wrong.
I've just seen on N.Geografic the accidents with the 737 rudder. The first accident and the incident happend like you said ,the 737 crossed some wake turbulance ,a jolt ,and the plane banked to left or right.
In the third case they were high ,and they had chance. Also ,the problem dissapeard by itself.
So, is the RSEP installed on your plane? This kind of occurence should be reported to aircraft manufacturer ,it may prove very important.
I can give you one example,happened 2 month ago ,big company,west europe.
" During flight control checks,a slight diff in pressure was felt on left ruddr.Then a kick was felt as the rudder was centerred and the Stby rudder light illuminated.After removing panels from the fin it was found that the rudder has not been modified to reflect the aircraft modification state "
Amazing ,right ?.
So ,make sure you report that to tech department,chief pilot,etc...be sure they found what was wrong.
Join Date: Oct 2004
Location: In a 737!
Posts: 30
Likes: 0
Received 0 Likes
on
0 Posts
Glad someone has brought this subject up. I have always meant to, but never quite got round to it!
I fly the 737NG and have found the A/P on to be a tad troublesome at times.
I've had 2 incidents recently that both went something like this; with the A/P recently engaged at N1 after t/o I had selected LVL CHG to climb the a/c at 250kts, to bypass the altitude restrictions in the FMC, as we had been cleared to a FL above the highest restriction on the SID by ATC. The A/P then had a brainstorm, having achieved 250kts it pulled the nose up quite normally but failed to stop at a NU pitch attitude appropriate to the speed, let the speed wash off alarmingly quickly and hit a maximum ROC of 6500fpm. I disengaged the A/P and brought it back under control, then re-engaged everything and the flight continued quite normally.
This then happened again the next day, in the same circumstances as before. Both incidents were reported in the tech log. Still have no idea why it happened though, didn't get any feedback at the time.
Anybody have any thoughts?
I fly the 737NG and have found the A/P on to be a tad troublesome at times.
I've had 2 incidents recently that both went something like this; with the A/P recently engaged at N1 after t/o I had selected LVL CHG to climb the a/c at 250kts, to bypass the altitude restrictions in the FMC, as we had been cleared to a FL above the highest restriction on the SID by ATC. The A/P then had a brainstorm, having achieved 250kts it pulled the nose up quite normally but failed to stop at a NU pitch attitude appropriate to the speed, let the speed wash off alarmingly quickly and hit a maximum ROC of 6500fpm. I disengaged the A/P and brought it back under control, then re-engaged everything and the flight continued quite normally.
This then happened again the next day, in the same circumstances as before. Both incidents were reported in the tech log. Still have no idea why it happened though, didn't get any feedback at the time.
Anybody have any thoughts?
Join Date: Aug 2005
Location: fairly close to the colonial capitol
Age: 55
Posts: 1,693
Likes: 0
Received 0 Likes
on
0 Posts
Shortly after LOC capture at KDEN in a -700BBJ, the A/P began commanding lateral excursions from right to left and back again, then reverted to CWS mode. Disconnected the A/P and flew the approach manually. FAA had no indications of LOC deviations. This was entered in the maintenance log.
Several days later after another flight, one of our VPs informed us that a fellow passenger was using his blackberry device around the time of the incident.
This sort of odd A/P behaviour is not limited to the 737, by the way.
Several days later after another flight, one of our VPs informed us that a fellow passenger was using his blackberry device around the time of the incident.
This sort of odd A/P behaviour is not limited to the 737, by the way.
Join Date: Mar 2002
Location: London
Posts: 52
Likes: 0
Received 0 Likes
on
0 Posts
Similar thing happened to me about 4 years ago. 737-300 at FL 360 or thereabouts on a very dark moonless night, FO was PF, quite new I recall. Gradually and smoothly and for no good reason the aircraft rolled left to about 5 or so degrees, stopped, then rolled right to about 10 degrees, stopped, then back to the left again. Only this time the roll to the left didn't stop and at 25 degrees AoB and merrily increasing I disengaged the autopilot and hand flew for a while. The thing flew well enough, all trims normal, so I put my autopilot on and it was fine, tried the FOs autopilot and that was fine too. Reported it on landing and nothing found.
Thread Starter
Join Date: Feb 2007
Location: Vancouver
Posts: 40
Likes: 0
Received 0 Likes
on
0 Posts
Thanks for your inputs so far. Reporting wise i did what was possible from my side. To get a better picture: The MCP was working fine, no blanks, no frozen digits. All modes selectable and responsive. The flight director did not command the roll. It started after the overtaking passed by but unfortunately i could not identify the type. What i can say is that this particular jolt felt very strange. To smooth for a hard wake and in my opinion not enough to kick out the autopilot at a sudden. Never felt something like this before.
hb
hb
Join Date: Mar 2002
Location: London
Posts: 52
Likes: 0
Received 0 Likes
on
0 Posts
Slightly off topic here, but talking of things going bump in the night.... climbing through the low FL300's, very smooth winters night, stars etc, when BANG , simultaneously the whole aircraft jumped, I could hear the galley, trolley crash. My first impression was we'd hit something, or maybe a bomb had gone off. Pushed to level off (A320) and waited for the ECAM to turn red.
Meanwhile the CSA 1 (senior hostie) came in to the flight deck thinking doomsday thoughts and I remember looking back down the aisle half expecting the floor to be caved in! (Read too many accident reports) A thorough check of all systems, cabin, showed nothing other than normal, so we continued on our way. ATC had no reported traffic near us at the time and nothing on TCAS. Wrote it up and filed an ASR, got a phone call quite a while later saying that there was nothing in any of the downloaded information to indicate anything had happened.
Meanwhile the CSA 1 (senior hostie) came in to the flight deck thinking doomsday thoughts and I remember looking back down the aisle half expecting the floor to be caved in! (Read too many accident reports) A thorough check of all systems, cabin, showed nothing other than normal, so we continued on our way. ATC had no reported traffic near us at the time and nothing on TCAS. Wrote it up and filed an ASR, got a phone call quite a while later saying that there was nothing in any of the downloaded information to indicate anything had happened.
Join Date: Aug 2004
Location: UK
Posts: 87
Likes: 0
Received 0 Likes
on
0 Posts
hbiwe - on which model 737 did the event happen?
For the Jurrasic & Classic, Service Letter 27-110A UNEXPECTED ROLL AND YAW EVENT TROUBLESHOOTING provides information which will aid operators in reporting and troubleshooting of just such an event.
There does not appear to be a similar document for Next Generation.
The tech people at your airline can get you a copy, assuming it applies model wise.
For the Jurrasic & Classic, Service Letter 27-110A UNEXPECTED ROLL AND YAW EVENT TROUBLESHOOTING provides information which will aid operators in reporting and troubleshooting of just such an event.
There does not appear to be a similar document for Next Generation.
The tech people at your airline can get you a copy, assuming it applies model wise.
Thread Starter
Join Date: Feb 2007
Location: Vancouver
Posts: 40
Likes: 0
Received 0 Likes
on
0 Posts
Terra, its a 737-500. I have been informed that the event recorder has been analyzed for a quick review but no evidence found. During the next days they will perform detailed analysis of the data and check more parameters. I will update as soon as i recieve the first report (if they can find anything)...
hb
hb
