Date: 201511
Local time of day: 1801-2400
Location: ZZZ.Airport, US
Light: Night
Aircraft: B737-800
Operator: Air Carrier
Operating under: Part 121
Flight plan: IFR
Mission: Passenger
Flight phase: Initial Approach
Airspace: Class B ZZZ
ATC / advisory: TRACON ZZZ
Aircraft component: Trailing Edge Flap
Component problem: Malfunctioning
Reporter organization: Air Carrier
Reporter function: Other / Unknown
Human factors: Workload; Situational Awareness; Training / Qualification; Troubleshooting; Human-Machine Interface; Fatigue; Distraction; Communication Breakdown
Anomaly: Aircraft Equipment Problem Less Severe; Deviation - Speed All Types; Deviation / Discrepancy - Procedural Published Material / Policy
Detector: Automation Aircraft Other Automation; Person Observer
When detected: In-flight
Result: Flight Crew Took Evasive Action; Flight Crew FLC complied w / Automation / Advisory
Contributing factors: Aircraft; Chart Or Publication; Human Factors; Procedure
Primary problem: Procedure

Narrative: On approach; while jumpseating; I noticed the flaps were not extending properly. The crew wasn't aware of the malfunction initially; and continued to slow to; and then well below; the speed for the desired flap setting; not realizing the wing was nearly clean. FO was hand flying. Shortly after I informed the crew of their flap problem; their speed further decayed. I called out the low airspeed/high AOA condition; and a few seconds later; the 'Airspeed Low' aural warning came from the aircraft. The FO recovered the aircraft from the approaching stall at approximately 2;400 feet on vectors for the approach. After the aircraft was back under control; the next problem was recognition and application of the appropriate flap malfunction checklist.Initially; I was very interested in looking out the windows; as I was about to fly my little plane over the same route over the mountains the next day; so my full attention wasn't on the crew in the beginning. That changed; however; as I felt the nose seemed higher than normal. I glanced forward and the flap needles being split caught my eye; looked up to see the yellow lights overhead; and then noticed the decaying airspeed. The FO was hand flying; which might have been a good thing if he had picked up on the abnormal pitch attitude sooner; but absent that; he would have been much better off with the autopilot selected; as the a/p would have maintained the 190KIAS selected in the airspeed window. The minimum speed reached was 172 KIAS with trailing flaps at 1/2 and 1 degrees; LED extension unknown; but indicating yellow on both the panel amber light and the overhead panel. From data available; I estimated the stall speed was only approximately 10 KIAS lower. As long as the autopilot was working and that speed selected; we shouldn't have been able to get any slower. Both crewmembers seemed tired and slow to react; in my opinion. I remember wanting to see the FO act more quickly; and I felt buoyed when the 'Low Airspeed' automated call reinforced my own call to get the nose down and reduce AOA. The FO continued to hand fly even after that; which added workload to the CA; as he had to monitor closely which detracted from his PNF duties and checklist attention. I'm hoping this makes its way to the training people. FO's in particular should be trained to talk; coordinate; and fly with good use of a/p all on their own allowing the PNF/PM to work the problem with minimal distractions. Instead of just a V1 cut; try a scenario like this to completion where both pilots are busy in their own roles.But once the problem was recognized and an appropriate speed attained/maintained; the immediate problem was over; but the flap issue remained. The CA was swamped with coordinating with ATC; monitoring his FO; and choosing the correct checklist for a flap problem. The checklists are known to be less than clear; as for years the sim's have pointed that out in recurrent; including my recent one; so I actually felt reasonably prepared for this event. Just the same; the first checklist that appeared to be appropriate was the Leading Edge Flaps Transit in the QRH based on the listed condition that the LED's were not in the commanded position. I was doing my best to back up the CA; and when he started with this checklist and before I got there; he repositioned the flap handle back to 1 or up; not sure but I'm thinking up. I wasn't happy with the checklist choice or the flap handle movement at that time; plus I was watching the FO and also the distracted CA; so as a group; we weren't in sync. After a short time; I became the checklist reader; so they both could fly. That checklist eventually directed us to Trailing Edge Flap Disagree. Somehow the CA and I ended up not diagnosing the less apparent asymmetry and proceeding on to step two; which called for alternate flap extension. I was concerned that by doing that; we had the potential of inducing a split flap configuration; but after identifying theabsence of any roll and continued absence during extension; I'm certain we would have not allowed anything more than a minor split; and in this case; it gave us a normal landing configuration of 15 flaps and corresponding LED's. But no question; we overrode a valuable protection system without appropriate consideration. Of note; there is no stop at 15 degrees; and the CA got distracted and was heading past that when I alerted him. It really worked out much better that we were a 3 man crew. With the super busy crew; I handled the FA comm; a not rushed passenger PA both prior to landing and after landing to keep control of the cabin while the CFR vehicles were in plain view and FAs were jittery. Once on the approach; I still wasn't thrilled with the checklist; and then I found the better choice; Trailing Edge Flap Asymmetry; where we should have started; but by then we were in a normal 15 flap configuration. So the end result was better; but our handling was admittedly incorrect.With this experience; I know the flap system far better than I did before. We first dodged a near stall; then potentially exposed us to a bigger asymmetry. Next time; I'll be the flap failure God; but this time; we didn't react well. This is why we train; and my guess is the vast majority of even long time 737 pilots would screw this checklist up also. Recommendations; all for training folks:1) Demand more from FO's (and CA's) so they can expect to talk and fly allowing the PNF to focus intently on the checklist.2) Stress how the a/p is your friend in these situations. A good FO with a working a/p is practically a whole crew alone. Practice that with typical ATC distractions; not the usual sim verbiage. 3) Take the time in the sim to freeze and point out what each variant of flap malfunction looks like and which checklist corresponds to the indications. 4) Management seems bent on these 3 leg 12+ hour days with 8+ hours flying; with our aging pilots; you're going to see degraded performance regularly. I saw signs of slow reactions that suggested this crew wasn't at their best.5) Redesign the checklists into a better flow chart. Simple 'Are trailing edge flap needles split?' kind of questions would help in the heat of the moment; as opposed to having us bite on the LED checklist which appeared attractive due to the 'condition' of the LED's not matching the flap handle. Obviously not the big picture; but with all the distractions and fatigue; clearly we fell for it. A real systems review in recurrent aligning what the checklists do with why from a systems point of view would be beneficial. Flying single seat in the military; we pretty much had to know every checklist; as it was very difficult to fly (no a/p on my old jets) and read. In training; ideally we should perform as many checklists as possible. Honestly; a V1 cut was way easier than this issue. We're practiced at the V1 cut; yet this felt like virgin territory.




Synopsis: A B737-800 Pilot observer detected a flap asymmetry before the crew who flew into an 'Airspeed Low' aural warning before recognizing the anomaly. The crew's actions that followed demonstrated the B737 ASYMMMETRY TRAILING EDGE FLAP Checklist pitfalls and confusion experienced by many crews.