GACFaja Posted June 25, 2009 Share Posted June 25, 2009 Good morning! We have a P model here that has a recurring porpoising issue with its AN/AYW-1 Autopilot. This aircraft has had a history of this for several years and in that time the elevator servo has been changed several times, numerous processors, air data sensor has been changed a couple of times, cable tensions checked/adjusted to the elevator servo, and at least two elevator boost packs. We have wrung the wiring out multiple times and also checked all the grounds for corrosion/paint, since another unit had a similar problem caused by painted-over grounds. The elevator trim relays were changed before the aircraft went into depot last year and the aircraft flew good for a few months and then the problem came back prior to its depot input. We got the aircraft back from depot a few months ago and the problem is still there. The TOPS panel shows no faults associated with the porpoising and we have also checked the wiring between the servo and processor, checked the ADS signals/wiring, and the MBIT 2 (ADS #1) and MBIT 19 (Elevator Sero Hyd) pass every time along with the full system operational checkout. Has anyone seen anything like this? I'd welcome any suggestions. Thanks! Quote Link to comment Share on other sites More sharing options...
bryanball Posted June 26, 2009 Share Posted June 26, 2009 Call the guys at 1 SOMXS on Eglin. The GCS shop there has some good experiance with long term autopilot problems. Quote Link to comment Share on other sites More sharing options...
timcoppin Posted June 27, 2009 Share Posted June 27, 2009 I saw this many, many moons ago on 60221. It was doing the same thing, only with the E-4 autopilot, and as well had been doing it for many years. The fix was found to be the elevator trim tab actuators (jackscrews). The maintenance books say to ops check them you run them up and down. What they wern't saying (and was figured out by another crew chief, Tony Jeffrey) was there needs to be an air load applied to the trim tabs whiole running them. Do this by allpying a small amount of pressure to the tab just aft of where the actuator attaches to it while running the tabs. What you will most likley hear is a banging coming from inside the elevator, at the forward end of the actuator. This is the internals of the actuators slipping. The actuators have no time change (we asked for this several years ago, late 1980's), and are a real "mother" to remove. I'd recommend removing the elevator and soaking the bolts with penetrating oil. We did this on 60223 in around 2001 when the banging was discovered on it. After a week of "whenever anyone walks by, squirt oil on the bolts", it still took using a rivet gun and angled rivet set to remove the bolts, as they were siezed in the rod end that rotates. Also, keep in mind, that the trim tab cables used to be a 6000 time change, don't know if they still are, and are usually "forgotten" due to the fun of replacing them, so this would be a great time to replace them, too. We asked for changes to the books several years ago, to add in the simulated air load and a time change for the actuators, but were ignored. Quote Link to comment Share on other sites More sharing options...
GACFaja Posted June 30, 2009 Author Share Posted June 30, 2009 Thanks for the suggestions! We're gonna give it a try--I'll keep you posted on the results. Quote Link to comment Share on other sites More sharing options...
tinyclark Posted July 13, 2009 Share Posted July 13, 2009 We had one doing this, and we finally changed out the A/P servo clutch, not just the servo. Quote Link to comment Share on other sites More sharing options...
GACster Posted July 22, 2009 Share Posted July 22, 2009 I work with GACfaja. We tried applying pressure to the trim tab with it moving in both directions and we didn't hear a thing. A/R came out for a rig check and said everything worked as advertised. Got any more suggestions? We're trying to get in touch with some people at Honeywell too. Quote Link to comment Share on other sites More sharing options...
Shadoif Posted July 26, 2009 Share Posted July 26, 2009 If memory serves me right.....(about 2004) went to pick one up at the rock after mod and after several days the contractor put some filters in the vor system that was causing feedback. Zak Quote Link to comment Share on other sites More sharing options...
Dan Wilson Posted July 27, 2009 Share Posted July 27, 2009 Wow Zak, your a junior member now:eek: who'd you piss off:rolleyes: Dan Quote Link to comment Share on other sites More sharing options...
tinyclark Posted July 27, 2009 Share Posted July 27, 2009 Zak, If memory serves me correctly, it was happening during ILS approaches, and they changed the large filter caps that are mounted on the back of the NIRP. The caps smooth out the Loc and G/S signals. GACFaja, Does the aircraft porpoise in all modes, and at all times? Quote Link to comment Share on other sites More sharing options...
Shadoif Posted July 30, 2009 Share Posted July 30, 2009 Yeah that was it, during the coupled approaches the porpoising was 200'! Quote Link to comment Share on other sites More sharing options...
tinyclark Posted July 30, 2009 Share Posted July 30, 2009 Whatever the instruments do, the autopilot will try to follow when it's coupled to them. That AP1 and AP2 is kind of confusing anyway, but the AP1 is pilot's intruments, AP2 is copilot's. Y'all probably knew that though. Quote Link to comment Share on other sites More sharing options...
GACFaja Posted August 26, 2009 Author Share Posted August 26, 2009 (edited) Zak, GACFaja, Does the aircraft porpoise in all modes, and at all times? Yep. AP1/AP2, basic autopilot, and Altitude Hold. She's been doing this since she came to us from Patrick in '02 or early '03. It starts oscillating, small at first, then worse...almost like it's missing the servo feedback. No associated bit faults, wiring Ohm's out great, op checks great on the ground. We write it up for an inflight check and she fails every time. We've gotten it to go away for as much as 6 months by changing the elevator pack. A 7-lvl flew with the aircraft--when the aircraft would porpoise the elevator trim indication would follow the porpoising, which it should since the autopilot uses the elevator trim to assist the surface. If the crew put an OPPOSITE input to the flight controls the porpoising would null out and stop for a while. Getting to the point of calling for a depot team. Or putting a grenade in the drybay.:D Edited August 26, 2009 by GACFaja Adding more info Quote Link to comment Share on other sites More sharing options...
GACFaja Posted August 26, 2009 Author Share Posted August 26, 2009 (edited) Duplicate post--can't delete it? Edited August 26, 2009 by GACFaja Duplicate post Quote Link to comment Share on other sites More sharing options...
tinyclark Posted August 27, 2009 Share Posted August 27, 2009 I assume the trim tab is trying to drive the aircraft back and not actually causing the condition. If I'm thinking right, if the aircraft starts to pitch up, the trim tab should go up, trying to force the elevator down. Is that what's going on? I never did see anything after I posted something about the servo clutch. Have you changed that out, and not just swapped the servo? Quote Link to comment Share on other sites More sharing options...
Guest Posted August 27, 2009 Share Posted August 27, 2009 Do Digital Autopilots porpoise in steps? It's all 1's and 0's, I've heard..... Quote Link to comment Share on other sites More sharing options...
Skip Davenport Posted August 27, 2009 Share Posted August 27, 2009 Do Digital Autopilots porpoise in steps? It's all 1's and 0's, I've heard..... must be a hick up 2 trying to get in on the action :) Quote Link to comment Share on other sites More sharing options...
tinyclark Posted August 27, 2009 Share Posted August 27, 2009 LMAO, that's microsteps. Quote Link to comment Share on other sites More sharing options...
Guest Posted August 27, 2009 Share Posted August 27, 2009 LMAO, that's microsteps. Depends on whether it's an LSB or an MSB. Quote Link to comment Share on other sites More sharing options...
GACFaja Posted August 28, 2009 Author Share Posted August 28, 2009 I assume the trim tab is trying to drive the aircraft back and not actually causing the condition. If I'm thinking right, if the aircraft starts to pitch up, the trim tab should go up, trying to force the elevator down. Is that what's going on? I never did see anything after I posted something about the servo clutch. Have you changed that out, and not just swapped the servo? The drum/bracket assy was changed out, but didn't help matters. I'm trying to get hold of the 7 lvl who flew with the acft (he's in ISO now) but I doubt he'd remember which way the trim drove. Maybe I can get the FE to watch the trim indication on the next inflight op check. Quote Link to comment Share on other sites More sharing options...
hydro101 Posted August 31, 2009 Share Posted August 31, 2009 Well I dont think the 7 lvl that flew with the acft is going to be much help. Quote Link to comment Share on other sites More sharing options...
tinyclark Posted April 6, 2010 Share Posted April 6, 2010 Did this problem get fixed? If so, what did it? Quote Link to comment Share on other sites More sharing options...
GACFaja Posted April 6, 2010 Author Share Posted April 6, 2010 Did this problem get fixed? If so, what did it? We put in for a 107 about a month ago--they had us check attitude indications, rigging, trim tabs jackscrews, and sim in flight with a 205 and jumpering the touchdown relay, then change out an elevator pack. The plane porpoised on the next flight and they had us change another pack. The aircraft flew up to Nellis last night--haven't heard about whether it porpoised. More later, I'm sure--we didn't find anything wrong on all the other checks and I don't think the pack is going to fix it either. Quote Link to comment Share on other sites More sharing options...
rdenn_58 Posted April 6, 2010 Share Posted April 6, 2010 Amazing how much info is lost in 4 years being away from it. Does the Radar Altimeter interface with the autopilot or is it all with pressure altimeters? Can you do a 205 leak check for the hoses at the air data hoses? Does this problem happen at all altitudes or is there a specific range that this occurs? Quote Link to comment Share on other sites More sharing options...
n1dp Posted April 7, 2010 Share Posted April 7, 2010 Years ago has a similar problem on a B model/E-4 Auto Pilot. Had the elevator loop all torn apart, rung out etc. The problem ended up being four bad "RFI" elevator servos from supply. Never trust anything. Quote Link to comment Share on other sites More sharing options...
tinyclark Posted April 8, 2010 Share Posted April 8, 2010 Amazing how much info is lost in 4 years being away from it. Does the Radar Altimeter interface with the autopilot or is it all with pressure altimeters? Can you do a 205 leak check for the hoses at the air data hoses? Does this problem happen at all altitudes or is there a specific range that this occurs? The AYW-1A (E4 replacement) uses its own digital altimeter encoder for ALT Hold. Quote Link to comment Share on other sites More sharing options...
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