MD-11
Flight Crew Air Transport Pilot (ATP)
Flight Crew Last 90 Days 50; Flight Crew Total 7000; Flight Crew Type 1800
Situational Awareness; Human-Machine Interface
Aircraft Equipment Problem Less Severe; Deviation / Discrepancy - Procedural Published Material / Policy
Flight Crew Became Reoriented; General Maintenance Action
Aircraft; Human Factors; Procedure
Upon logbook review; I noticed that the aircraft had multiple instances of the Level 2 Flap Disagree alert appearing during flap extension on final along with flap indicating errors.  Flap extension on the ground was normal for departure as was flap retraction after takeoff.  During an aircraft status review inflight we noticed that the left outboard flap had an amber x displayed during flight with the left inboard showing 0.  The captain of the flight and I discussed the possibility of the Level 2 Flap Disagree alert occurring on our final approach.  During flap extension on final; the flaps tracked normally to the requested position of 15 degrees; then shortly after; the Level 2 Flap Disagree alert displayed.  Upon selecting the configuration synoptic; the flap position displayed 20/14/15/14.  We referenced the Level 2 Flap Disagree checklist; which directs the crew to place the flaps to the last symmetrical condition; which in this case would be Flaps 0.  The intent of this checklist is to deal with a flap panel that jams without continuing to its requested position.  This was not the case in this instance where the flap that was causing the Disagree alert was extending symmetrically; but then slightly overextending enough to trigger the alert.  Additionally; when the autopilot was disconnected during configuration no asymmetrical roll moment was noticed; leading the crew to believe it was an indication error.  With this mind set; we opted to continue flap extension to landing flaps with the final indication of 50/37/37/35.  We determined that the risks of landing with Flaps 0 far outnumbered the risks of continuing with the Flap Disagree alert and opted to operate outside of the AOM Level 2 Flap Disagree procedure.
The aircraft we were operating; had been written up on the previous two flights for a level 2 'Flap Disagree' message involving the left outboard flap overextending beyond its commanded position. My first officer and I operated the previous flight. According to maintenance as indicated by corrective action described in the aircraft maintenance logbook; correct and symmetrical flap operation was verified prior to our previous flight and a problem had been found with the transmitting unit for the left outboard flap position indicator. On approach on our previous flight the following scenario occurred: Upon extension of landing flaps 35 at about 1500 feet AGL on approach; a level 2 'Flap Disagree' was displayed with the outboard left flap indicator displaying 40 degrees. At this point we were fully configured to land on a stable approach and absolutely no un-commanded roll was experienced. Based on problems with the left outboard flap transmitter on the previous flight; the lack of any adverse flight characteristics; and the fact that normal and symmetrical flap operation had been verified by maintenance immediately prior to our departure; it was our opinion that the flap position was correct and the problem continued to be with the transmitting unit. It is my belief that an abnormally configured and high speed landing with less than landing flaps represented a more significant safety threat than continuing a fully stabilized approach with an aircraft that was handling entirely normal so I decided to continue the approach to landing. What's more; any further repositioning of the flaps with a faulty position transmitter would be still be subject to inaccurate position indications. At no time were any operating speeds or limitations exceeded. Maintenance later verified normal flap operations on the ground and again focused repairs on a faulty data transmitting unit. On our next flight with this aircraft; we noted that once again correct and symmetrical flap operation had been verified by maintenance as a corrective action from our previous night's entry in the aircraft maintenance logbook. Once more; maintenance identified and tried to correct a problem with the left outboard flap indicator position transmitter. When we reached cruise; although no alert was displayed; my First Officer noted that the left outboard flap position indicator was no longer supplying a signal to the flap position indicating system as indicated by a yellow 'X' being displayed in the left outboard box on the system display 'configuration' page. We interpreted this to mean that left outboard flap indicator was either inoperative or once again unreliable. We took the time to discuss the situation and review pertinent checklists and the aircraft systems manual and briefed our possible actions in the likely event we would experience a further anomaly when we configured the flaps for landing. Because maintenance had verified normal and symmetrical flap operations before this and the previous leg; a known recurrent issue with the left outboard flap position transmitter; and the fact that the suspect flap indication appeared to be failed; it was our belief that another disagree message in the absence of any adverse flight control issues was very probably another indication error. Since a level 2 'Flap Disagree' message is only as valid as the data being supplied to the flap indicating system; a bad transmitter unit would therefore render the level 2 message erroneous. I believe that predicating any checklist or configuration action based on known false; or highly suspect data would represent an unsafe situation. When we configured the aircraft to landing flaps 35 on approach we once again received a Level 2 'Flap Disagree' messages. On this occasion the left outboard flap position varied from a brief yellow 'X'; to values between 47 and 50.The first officer who was the FP reported no substantial un-commanded roll inputs and the aircraft was flying normally. Based on our discussion of known previous issues; the continued erratic indications of the left outboard flap indicator and the fact that the aircraft was stably established on rather short final; we decided to continue the approach to landing. As with the previous occurrence; it was my opinion that any configuration change or checklist procedure using invalid data was pointless and that an abnormal high- speed approach with minimal or no-flaps represented a far greater safety risk than continuing the approach to landing. Like before; at no time were any speeds or limitations exceed and preliminary inspection of the aircraft flaps on the ground seemed to indicate no actual asymmetry.
MD-11 flight crew describes operating a flight that routinely displays a flap disagree message when flaps are extended during approach. Believing (correctly) that a faulty flap sensor is responsible for the message the QRH procedure is not followed and the message is ignored.