B737-800 air carrier flight crew reported receiving a low altitude alert from ATC while on approach after an Autoflight malfunction. The Captain performed a missed approach and safely landed on the second approach.
Synopsis
B737-800 air carrier flight crew reported receiving a low altitude alert from ATC while on approach after an Autoflight malfunction. The Captain performed a missed approach and safely landed on the second approach.
Narrative
We were clear for the ILS XR approach at ZZZ; weather at the time was 500 broken; 900 overcast visibility 6 miles with light rain. The base turn vector was at 3;000 feet and we were vector just outside the final approach fix to capture at 3;000 feet and final approach fix was at 1;800 feet. Before been established on the LOC the glide slope went immediately to the full down position; a small amount of vertical speed was used in order to capture; the LOC never capture and we slightly over shoot the final approach course; at that point the Captain disconnected the Autopilot and subsequently lost all flight director guidance on his PFD (Primary Flight Display) and HUD. An attempt was made by the Captain to re established the approach but was unable and subsequently pass the flight controls to the First Officer (FO). Try to re-establish the approach but was unable and immediately called for a go-around. ATC assigned to track the LOC inbound and to climb to 2;000 feet. Toga was pressed but auto throttles did not respond despite being on go around mode at that point [priority handling was requested] during this period ATC advised us of a low altitude alert and we very quickly established a climb to the newly assigned altitude of 3;000 feet. At this point we were trying to determine if we were receiving erroneous navigation information we were comparing FO's PFD information with the standby instrument to verify we determined that the FO PFD was accurate and then the FO took over as pilot flying. At this point ATC inquired as to the nature of the [problem] and we stated that we had solved our navigation problem. At this point we were vector to join the approach ran all the normal checklist and landed without any incident. Maintenance was notified in an AML (Aircraft Maintenance Log) entry was made and before leaving the aircraft we spoke with a mechanic personally about the malfunction.Close vector to the final approach fix; malfunction of the flight directors on the pilot flying side at a critical phase of flight in IMC conditions.Suggestions: Vector not so close to the final fix.
Second reporter narrative
We were clear for the ILS XR approach at ZZZ; weather at the time was 500 broken; 900 overcast visibility 6 miles with light rain. The base turn vector was at 3;000 feet and we were vector just outside the final approach fix to capture at 3;000 feet and final approach fix was at 1;800 feet. Before been established on the LOC the glide slope went immediately to the full down position; a small amount of vertical speed was used in order to capture; the LOC never capture and we slightly over shoot the final approach course; at that point the Captain disconnected the Autopilot and subsequently lost all flight director guidance on his PFD (Primary Flight Display) and HUD. An attempt was made by the Captain to re established the approach but was unable and subsequently pass the flight controls to the First Officer (FO). Try to re-establish the approach but was unable and immediately called for a go-around. ATC assigned to track the LOC inbound and to climb to 2;000 feet. Toga was pressed but auto throttles did not respond despite being on go around mode at that point [priority handling was requested] during this period ATC advised us of a low altitude alert and we very quickly established a climb to the newly assigned altitude of 3;000 feet. At this point we were trying to determine if we were receiving erroneous navigation information we were comparing FO's PFD information with the standby instrument to verify we determined that the FO PFD was accurate and then the FO took over as pilot flying. At this point ATC inquired as to the nature of the [problem] and we stated that we had solved our navigation problem. At this point we were vector to join the approach ran all the normal checklist and landed without any incident. Maintenance was notified in an AML (Aircraft Maintenance Log) entry was made and before leaving the aircraft we spoke with a mechanic personally about the malfunction.Failure of Captain's flight director. ATC give early base turn and an intercept vector that put our aircraft very close to the final approach point at a high altitude. Suggestions: Question ATC on poor vectors
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Source: NASA Aviation Safety Reporting System (public domain). Reports are voluntary submissions and are not verified by NASA.