Date: 201512
Local time of day: 1801-2400
Location: ZZZ.Airport, US
Flight conditions: Marginal
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: Tower ZZZ
Aircraft component: Autopilot
Component problem: Malfunctioning
Reporter organization: Air Carrier
Reporter function: Pilot Flying; Captain
Reporter qualification: Flight Crew Air Transport Pilot (ATP)
Human factors: Confusion; Distraction; Fatigue; Situational Awareness; Time Pressure; Workload
Second reporter function: First Officer; Pilot Not Flying
Anomaly: Inflight Event / Encounter Unstabilized Approach
Detector: Person Flight Crew
When detected: In-flight
Result: General None Reported / Taken
Contributing factors: Aircraft; Human Factors
Primary problem: Human Factors

Narrative: We were established on the localizer to the ILS approach. As we were approaching the FAF with the glide slope indication of a half dot above the aircraft; I as the Pilot Flying; called for gear down and flaps to 15. At the point that I thought the Pilot Monitoring lowered the gear; the autopilot and auto throttles suddenly disconnected. At that point; I tried to figure out why and didn't noticed that I went through the glide slope to being above the glide slope. I then applied correction to recapture the glide slope. When I adjusted pitch and power to capture glide slope; I then noticed that the flight director was not showing in the PFD. Having directional information still showing in the HUD and having clear sight of the runway; runway lights and approach light; I elected to continue with hand flying using the HUD and PAPI lights. I then began to notice that I was getting below the glide slope and began to correct too much and went above it again. By 1000 feet; I elected to continue because I still had the runway environment in sight and was correcting back to the glide slope. By 500 feet; I was still correcting to the glide slope that was below the aircraft; and because airspeed was under control and still in visual conditions; continued to correct pitch to catch glide slope and then got an aural 'SINK RATE' announcement. Made necessary pitch adjustment; landed under better control in touchdown zone. I know; in hindsight; that I should have gone around on a couple of locations on the approach because I was not stable. I fully admit that my false sense of desire to salvage the unstable approach caused me to make the poor decision to not go around throughout the approach.


Second narrative: I was the Pilot-Monitoring in a B737. We were given a RNAV Arrival; and then we were vectored to intercept the LOC for the approach. Our set up for the approach was good and we were 'in the green'.The Captain was the Pilot Flying at the time. Approaching the FAF we had the autopilot and the auto throttles on. Airspeed was approximately 180 KIAS with the flaps at 5. The LOC was captured and the Glideslope was alive. At 1/2 dot below the glideslope the CA called for 'Gear Down' and just as I reached up to extend the gear; the autopilot and auto throttles disconnected; and the PFD flight director command bars went out of view. I extended the gear and we set the flaps to 15. I experienced the 'swimming in glue' feeling of trying to understand what had happened to our well set up approach.The CA continued flying raw data; hand flying the aircraft and throttles with no flight directors. I began calling out deviations; LOC tracking and airspeed were good; but glideslope tracking was problematic. I called 'Glideslope' when initially we were slightly low (approx. 1/2 dot) and then called 'Glideslope' again as we became one and then 2 dots high.Our before landing checklist was complete and we were fully configured before 1000 feet AGL. We still did not have flight director guidance on the PFD's and the captain was hand flying the airplane and the throttles. The CA called for me to reset the flight director switches; but we still couldn't make the flight directors work for us. At this point we had the runway in sight and we were still too high. The captain called correcting but in hindsight I should have called for a go around. We were too high and we were descending too rapidly; it was not a stabilized approach.


Synopsis: The B737 crew experienced an autopilot and autothrottle disconnect at glideslope intercept; which led to an unstable approach. The Captain elected to land.