The flight crew of a Boeing transport received a TE FLAP DISAGREE EICAS message on short final; executed a go around and ultimately diverted to land on a longer runway.
Synopsis
The flight crew of a Boeing transport received a TE FLAP DISAGREE EICAS message on short final; executed a go around and ultimately diverted to land on a longer runway.
Narrative
We were cleared for a visual approach. At the FAF; I called for gear down; Flaps 20 and target speed. After the 1;000 foot call; I called for flaps 25 and continued slowing to target speed of approximately 155 KTS. When the flaps reached 25 degrees on the flap gauge; we noticed a Trailing Edge Flap Disagree lite on the forward EICAS. We executed a go-around to trouble shoot the problem. As we brought the flap handle to 20 degrees on the go-around; the TE Flap Disagree lite extinguished. We cleared the traffic pattern and attempted flaps 25 again to be sure that it wasn't a one time event. The TE Flap Disagree EICAS message appeared again so we went back to Flaps 20 and the EICAS message disappeared. The flap handle remained at flaps 20 and matched the actual flap setting of 20 deg. We completed the TE Flap Disagree irregular procedure and then contacted Dispatch and Maintenance Control for some input. After conferring with them and reviewing our configuration and landing performance requirements; we concurred that the most prudent course of action was to divert [to a longer runway location]. Our approach and landing was uneventful at a landing speed of approximately 164 KTS.
Second reporter narrative
There was no rolling moment or any aerodynamic differences noted. We waited a while to see if there was a lagging flap indicator-needle movement. Approaching 500 FT we went missed approach; positioned flap lever to 20; raised and gear all ops were normal. I checked the fuel totalizer which I recall as being 16.6. I took PF duties; co-ordinated flying in the airport vicinity and had the First Officer to go to the book and contact dispatch for a patch to Maintenance Control. We landed with totalizer fuel of 5.8. LH fuel 3.5; RH fuel 2.3. The burn from 88 NM to divert point at Flaps 20; altitude 7000 FT burned 4600 LBS of fuel. The TE Flap Disagree procedure has long been a seeming non-sequitur; rambling and; as I recall; perhaps re-written over the years. Maybe that's just the way it has to be. This having been said; what gave me pause was [what happened when] we were in the most predictable environment for encountering this irregularity; i.e. configuring for landing. At Flaps 20 we deployed the landing gear then went to Flaps 25 and got the disagree light. Since we were in the groove on a visual approach and had an irregularity the First Officer performed a procedurally correct Missed Approach Procedure: i.e. [TOGA thrust]/Flaps 20; positive rate of climb; gear up; which extinguished the EICAS warning! Now the disagree light was out and we were on the go. This all made sense to me in the dynamic environment. Now; however; we are at 7;000 with no Disagree light and the book out and the procedure says 'do not move the flap lever back to the flaps 20 position!' You simply do not have the book out; open to the correctly identified irregular page (not as simple as it sounds) with all cautions read and understood prior to performing your first duty; executing a proper Missed Approach Procedure. I knew I had a problem; but now I have no indications of a problem - i.e. the disagree light is out and the flap handle matches the indicator at 20 due to my positioning the flap handle to 20 as part of the Missed Approach Procedure which had to be performed without the Flight Handbook out when we were 'in close.' This is somewhat awkward to express clearly; but I was attempting to apply an Irregular Procedure to a problem for which I no longer had indications (but knew I had)! [I further discovered] after the fact; that my previous actions had violated a Procedural Caution that I hadn't yet read about...had extinguished the indication of the problem which required the use of the long; conditional; sequential; somewhat counter-intuitive Irregular Procedure required by that no longer active warning was somewhat Kafkaesque!
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Source: NASA Aviation Safety Reporting System (public domain). Reports are voluntary submissions and are not verified by NASA.