Mechanic reporter states that the autoplt mod on a particular aircraft renders the autoplt inoperati...

Narrative:

On dec/tue/89 deferral (autoplt porpoises in flight and vertical speed inoperative) expired. I was able to sign off the autoplt by replacing a fuse on the back side of the flight control computer black box (without disconnecting static lines) and cleaning pins with lps electrical contact cleaner on the stabilization computer and the autoplt control head. Replacing the fuse also fixed the 'yaw damper' which was deferred as 'yaw damper inoperative'. I did not sign off deferral until dec/mon/89 until I got a report back from the crew that the yaw damper worked satisfactorily. The problem is that heavy transport is a former air carrier plane and modified the autoplt under a coa and the overhaul facilities are doing something to the mod which causes the autoplt to be erratic or inoperative a lot. Due to the mod being tampered with, if the autoplt does not engage you can turn and hold the pitch selector knob slightly clockwise while engaging the autoplt lever and the autoplt will engage and work. But the autoplt should engage without having to turn the pitch selector knob. This is how I was able to clear the deferred item. Replacing the fuse allowed the yaw damper to engage and manipulating the autoplt control head allowed the autoplt to engage and work. The crew was not totally satisfied with the fix, but agreed to take the aircraft to yip because the company had hired a person to repair the autoplt by removing the air carrier mod and returning the aircraft to original design specifications. During the 4 hour flight from lax to yip the autoplt disengaged and would not reengage so the crew wrote up a discrepancy for the autoplt in yip and it was deferred. I'm sending in this report because I feel the fix I did on the autoplt was a 'gray area repair' meaning that the autoplt worked, but it did not work exactly as designed because of the united mods and having to manipulate the control head to get the autoplt to engage and I want the facts of the matter to be on record.

Original NASA ASRS Text

Title: MECHANIC REPORTER STATES THAT THE AUTOPLT MOD ON A PARTICULAR ACFT RENDERS THE AUTOPLT INOPERATIVE. A METHOD OF MAKING OR FORCING THE AUTOPLT TO ENGAGE WAS USED BY MECHANIC TO ENABLE A SIGN OFF OF REPAIR. MECHANIC HAS SECOND THOUGHT REGARDING VALIDITY OF TECHNIQUE AND SIGN OFF.

Narrative: ON DEC/TUE/89 DEFERRAL (AUTOPLT PORPOISES IN FLT AND VERTICAL SPEED INOP) EXPIRED. I WAS ABLE TO SIGN OFF THE AUTOPLT BY REPLACING A FUSE ON THE BACK SIDE OF THE FLT CTL COMPUTER BLACK BOX (WITHOUT DISCONNECTING STATIC LINES) AND CLEANING PINS WITH LPS ELECTRICAL CONTACT CLEANER ON THE STABILIZATION COMPUTER AND THE AUTOPLT CTL HEAD. REPLACING THE FUSE ALSO FIXED THE 'YAW DAMPER' WHICH WAS DEFERRED AS 'YAW DAMPER INOP'. I DID NOT SIGN OFF DEFERRAL UNTIL DEC/MON/89 UNTIL I GOT A REPORT BACK FROM THE CREW THAT THE YAW DAMPER WORKED SATISFACTORILY. THE PROBLEM IS THAT HVT IS A FORMER ACR PLANE AND MODIFIED THE AUTOPLT UNDER A COA AND THE OVERHAUL FACILITIES ARE DOING SOMETHING TO THE MOD WHICH CAUSES THE AUTOPLT TO BE ERRATIC OR INOP A LOT. DUE TO THE MOD BEING TAMPERED WITH, IF THE AUTOPLT DOES NOT ENGAGE YOU CAN TURN AND HOLD THE PITCH SELECTOR KNOB SLIGHTLY CLOCKWISE WHILE ENGAGING THE AUTOPLT LEVER AND THE AUTOPLT WILL ENGAGE AND WORK. BUT THE AUTOPLT SHOULD ENGAGE WITHOUT HAVING TO TURN THE PITCH SELECTOR KNOB. THIS IS HOW I WAS ABLE TO CLEAR THE DEFERRED ITEM. REPLACING THE FUSE ALLOWED THE YAW DAMPER TO ENGAGE AND MANIPULATING THE AUTOPLT CONTROL HEAD ALLOWED THE AUTOPLT TO ENGAGE AND WORK. THE CREW WAS NOT TOTALLY SATISFIED WITH THE FIX, BUT AGREED TO TAKE THE ACFT TO YIP BECAUSE THE COMPANY HAD HIRED A PERSON TO REPAIR THE AUTOPLT BY REMOVING THE ACR MOD AND RETURNING THE ACFT TO ORIGINAL DESIGN SPECS. DURING THE 4 HR FLT FROM LAX TO YIP THE AUTOPLT DISENGAGED AND WOULD NOT REENGAGE SO THE CREW WROTE UP A DISCREPANCY FOR THE AUTOPLT IN YIP AND IT WAS DEFERRED. I'M SENDING IN THIS REPORT BECAUSE I FEEL THE FIX I DID ON THE AUTOPLT WAS A 'GRAY AREA REPAIR' MEANING THAT THE AUTOPLT WORKED, BUT IT DID NOT WORK EXACTLY AS DESIGNED BECAUSE OF THE UNITED MODS AND HAVING TO MANIPULATE THE CONTROL HEAD TO GET THE AUTOPLT TO ENGAGE AND I WANT THE FACTS OF THE MATTER TO BE ON RECORD.

Data retrieved from NASA's ASRS site as of August 2007 and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.

Attributes
ACN	131285
Time
Date	198912
Day	Tue
Local Time Of Day	1801 To 2400
Place
Locale Reference	airport : lax
State Reference	CA
Altitude	agl bound lower : 0 agl bound upper : 0
Environment
Flight Conditions	VMC
Light	Night
Aircraft 1
Operator	common carrier : air carrier
Make Model Name	Heavy Transport, Low Wing, 4 Turbojet Eng
Flight Phase	ground : preflight
Flight Plan	None
Person 1
Affiliation	company : air carrier
Function	other personnel other other personnel other
Qualification	other other : other
ASRS Report	131285
Person 2
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : atp
Events
Anomaly	aircraft equipment problem : less severe
Independent Detector	other flight crewa other other : unspecified
Resolutory Action	none taken : unable
Consequence	Other
Supplementary
Primary Problem	Aircraft
Air Traffic Incident	other

Mechanic reporter states that the autoplt mod on a particular aircraft renders the autoplt inoperative. A method of making or forcing the autoplt to engage was used by mechanic to enable a sign off of repair. Mechanic has second thought regarding validity of technique and sign off.