Date: 201504
Local time of day: 0001-0600
Location: SFO.Airport, CA
Flight conditions: VMC
Aircraft: B737 Undifferentiated or Other Model
Operator: Air Carrier
Operating under: Part 121
Flight plan: IFR
Flight phase: Parked; Taxi
Aircraft component: FMS/FMC
Component problem: Malfunctioning
Reporter organization: Air Carrier
Reporter function: Pilot Not Flying; Captain
Human factors: Human-Machine Interface; Troubleshooting; Training / Qualification
Anomaly: Aircraft Equipment Problem Less Severe; Deviation / Discrepancy - Procedural Clearance; Deviation / Discrepancy - Procedural Published Material / Policy
Detector: Person Flight Crew
When detected: Taxi; In-flight
Result: Flight Crew Became Reoriented; Flight Crew Returned To Clearance
Contributing factors: Human Factors; Aircraft
Primary problem: Ambiguous

Narrative: During cockpit prep; First Officer (FO) loaded winds into FMC. I verified this before loading departure and arrival info into FMC. Once PDC received; I put in new SID transition and verified all SID and STAR crossings; with FO's input. At gate; we received well over 15 final weight messages across printer; followed by almost as many messages from load planning invalidating weights (for cargo change and then waiting for ramp to finalize weights.) After about ten minutes of this; I called Operations to tell them we were waiting for correct weights. They checked with ramp and said final weights should be forthcoming. The weights that came were different by only about 300 LBS (not significant; in my mind). We pushed. The FO kept waiting for the weights to upload into the FMC; but they would not. We tried referencing the flight manual but there was no guidance about how to proceed. Fired a message to dispatch; who could not provide assistance. Asked FAA jumpseater; a maintenance inspector familiar with our aircraft. He said he'd seen this once before and it required a complete re-initialization.  We tried manually entering weights; but VNAV wouldn't arm; so we were stuck. I thought about wind requests filling the buffer and blocking further action; and we discussed that; but agreed winds had only been requested once and already executed. Still; FO checked route data page and noticed an erase prompt. He selected it and immediately; the final weights uploaded. We got takeoff data; and off we went. Once airborne; ATC gave us headings followed by clearance direct to fix on SID. That is when I realized our cleared SID and transition were gone and the original SID was in FMC. I quickly reloaded correct SID and checked rest of route. The STAR; with RWY and transition were also missing! We all had seen these entries confirmed and executed at the gate; even the FAA guy confirmed this; so how they went missing is a mystery. The FAA guy encouraged me to write this report; because the whole thing was so screwy; and set us up for a potential navigation deviation. I referenced the QRH and sent a MISC report using the ND (Navigation Display) code; typing 4 pages of explanation. What I got back was a message saying that QRH code was not supported by this ACARS; or something like that. So the QRH codes are useless on this fleet (who knew?) this entire debacle with a [FAA employee] onboard was stressful; and pointed out the lack of guidance in our manuals dealing with such anomalies. The FMC shouldn't be so quirky; or 'inaccessible' for pilot intervention during malfunctions.




Synopsis: B737 Captain reports being unable to upload weight and balance information into the FMC until an erase prompt is noticed on the route page and pressed. Once airborne it is determined that the erase prompt has removed all the route changes made at the gate. The SID is quickly reentered.