B737-700
Flight Crew Air Transport Pilot (ATP)
Flight Crew Last 90 Days 415; Flight Crew Type 14000
Aircraft Equipment Problem Less Severe; Deviation / Discrepancy - Procedural Published Material / Policy
Air Traffic Control Provided Assistance; Flight Crew Executed Go Around / Missed Approach; Flight Crew Requested ATC Assistance / Clarification; Flight Crew Landed in Emergency Condition; Flight Crew Overcame Equipment Problem
Aircraft
While on final approach; and after selecting the final landing flaps of 40; I called for the Before Landing Checklist. Before the checklist was initiated; I noticed that the flap gauge indicated an asymmetrical flap indication with the right flap locked at 8 degrees and the left flap locked at 12 degrees. The flap handle was in position 40. I announced the problem and told the First Officer to inform the Tower we were going around. We initiated a go-around to 3000 ft and requested delay vectors out to the east of the field to handle the flap problem. We completed the QRH Trailing Edge Flap Asymmetry Checklist. In accordance with the checklist the flap handle was moved to position 5 and VREF/VTARGET were calculated (153/158). The performance computer was still operational so we used it for performance calculations and landing data. The performance computer indicated the best stopping margin was approximately 700 ft. I made several PA's to explain the situation to the Passengers and also spoke to the Flight Attendants over the service interphone. I initially had trouble communicating with my Dispatcher via ACARS as it was either ACARS NO COMM or had ceased working. Eventually I communicated with my Dispatcher over the Ops frequency and he agreed with our decision to land. The ACARS problem eventually cleared itself before landing; but by then performance weight and balance was not utilized or needed. The performance computer indicated that brake cooling was a consideration and to inspect the fuse plugs after landing. Due to the brake cooling factor; I elected to [advise ATC] and requested Fire and Rescue be available for a possible brake issue after landing. We flew the RNAV Approach and landed uneventfully; cleared the runway; and stopped on the taxiway. When the Fire Department confirmed there was no smoke or visible problems with the tires or brakes we requested the Fire Department follow us to the gate. The First Officer requested via Ops that the Ramp chock our nose tires but to not approach the cargo bins or tires until the go-ahead by the Fire Department. The logbook was filled out for both the flap issue and for brake energy/brake cooling concerns. The Fire Department measured the brake temperature at the gate and I spoke with the Fire Chief briefly. At that time; I was told that the brake temperature was in the normal readings; however; Ops later informed me that the Ramp was not allowed to approach the cargo bins for approximately an hour. So; maybe they had another concern about the brake temperature after I spoke with them? I coordinated with all applicable parties (Airport; Fire Department; Dispatch; Chief Pilot on Call; MX Control) and handed the aircraft over to Mechanics. I have two general Safety concerns: ACARS issues and differences between the performance computer data and performance weight and balance. During this event I attempted to request voice contact with my Dispatcher via ACARS. After no contact for a period of time we noticed that our ACARS messages were not transmitting. This not only hindered our ability to communicate and obtain data from our Dispatcher but degraded the ability to utilize the performance weight and balance system for performance review. Thankfully; the performance computer was still operational and allowed by OPSPEC. The ACARS eventually transmitted all of our messages in mass but this did not occur until on final approach.Additionally; the Wi-Fi system is inconsistent and often our EFB's lose the connection which would render our application useless. I have a Safety concern about all of our performance data in a non-normal situation being placed upon either ACARS or the Wi-Fi; both of which operate inconsistently in our aircraft. Additionally; later in the day I compared the Asymmetrical TE Flaps (flap L VR 1 to <15) landing data between the performance computer and the performance weight and balance system. I noticed some significant differences. The performance computer indicated 720 ft of stopping margin and the performance weight and balance indicated 439 ft of stopping margin. Also; the performance computer indicated 54 minutes of brake cooling time were needed with 29.7 million feet/pounds of energy being generated. The performance weight and balance indicated 39 minutes of brake cooling and 24.8 feet/pounds of energy being absorbed by the brakes. This significant difference between the performance computer and performance weight and balance in a non-normal landing configuration was puzzling. Is the performance weight and balance performance using different braking calculations than the performance computer? It seems like deceleration braking data would be the same for both performance engines? Finally; a strange occurrence developed with this aircraft. The flaps indicated an asymmetrical condition (right flap 8 degrees/left flap 12 degrees) the entire time we were airborne during this event. However; after landing and clearing the runway we observed the flaps retracting symmetrically to position 5; the position of the flap handle. The flaps retracted on their own without any input from the cockpit. I expected the trailing edge flaps to be locked due to the flap slat electronic unit closing the TE flap bypass valve. I explained the observation of the flaps retracting to position 5 after landing to the Mechanics and they were equally puzzled.
[Report narrative contained no additional information.]
Boeing 737 flight crew reported that the trailing edge flap indicator indicated split flaps; with no unusual aircraft movements.