Air carrier First Officer reported receiving a low altitude alert from ATC on approach into OAK after confusion with an ATC clearance.
Synopsis
Air carrier First Officer reported receiving a low altitude alert from ATC on approach into OAK after confusion with an ATC clearance.
Narrative
Tower informed us that they received an altitude alert while we were on approach to Runway 30. As the Pilot flying (PF); I got behind and lost situational awareness (SA) which caused us to get slow and high. We trended well above GS. The First Officer (FO) called out slow speed and suggested flaps. They also suggested dropping the gear to get down. All great suggestions; which we completed immediately. We descended at a higher than normal rate to acquire GS; at approximately 1700 ft. AGL. Tower informed us that they received an altitude alert on us. I believe it was due to our rate of descent. I over corrected and descended slightly below glide slope (one white and 3 red) then made the necessary corrections to acquire 2 white and 2 red PAPIs. We were stable by 500 ft. and continued to land without incident. Descending through approximately 18000 ft.; Approach canceled speed restrictions and cleared us for the approach. I focused on the speed restriction deletion and did not hear that we were cleared for the approach. I then made an attempt to delete the speeds in the FMS as the PF (mistake). I lost SA where we were relative to the path because I was focused on deleting 'vectors' in the FMS in order to join a common point on the arrival and approach. My focus on the FMS contributed to my loss of SA. Fortunately; the FO was way ahead of the jet and error captured all of my mistakes. They did a fantastic job.
Second reporter narrative
Descending via the OAKES 2 arrival into OAK landing at Runway 30 we are switched to NorCal Approach. Checking in with NorCal Approach ATC deletes the speed restrictions on the arrival and clears us for the ILS Runway 30 roughly 60 NM away from the airfield. Upon reaching the last fix in the arrival 4500 ft. MSL (8.2 NM from FAF) NorCal Approach switches us to Oakland Tower; the Captain then asks me to return to Approach frequency to ask if we are getting vectors for the ILS. I inform the Captain that we have already been cleared for the ILS approach. The Captain proceeds to go heads down to sequence the next fix in the FMS and does not lower the Mode Control Panel (MCP) altitude to the FAF altitude causing the jet to remain at 4500 MSL. Simultaneously the jet has sequenced to slow to the FMS speed of 170 kts. associated with the FAF. Before the Captain can sort out the next fix in sequence the jet has slowed to 200 kts. in a clean configuration causing the low airspeed alert to activate. At this moment I ask the Captain if they would like me to extend the flaps. As I begin to extend the flaps to the 5 descent the Captain disconnects the autopilot in order to correct for being high and steep on the approach. Gear is lowered to increase drag to help with the descent and I begin configuring the airplane and adjusting the speed to get onto the correct approach speed while the Captain is correcting for the high steep approach. Fully configured at flaps 30 and gear down the flight path is correcting to a normal 3 degree approach wire but the correction was held too long causing Oakland Tower to issue an aircraft low warning. The Captain levels off momentarily and intercepts the correct 3 degree approach and the flight lands without any further incident.The cause of this is a poor shared mental model of the clearance received and the aircraft energy state and a breakdown in the separation of pilot flying and pilot monitoring duties. The shared mental model broke down upon being cleared for the ILS when initially checking in with Approach. We could have done a better job to ensure that both pilots were aware of the clearance that was issued. Additionally as the pilot monitoring I could have been more proactive to verbalize the deviations of the aircraft flight path from the correct path and not allow the Captain to go heads down in the FMS as the pilot flying. As the approach progressed it was apparent the pilot flying was behind the jet and struggling to get ahead of the aircraft. The correct action should have been a discontinued approach and get vectors for another approach into the airport. A thorough understanding of the clearance and where the aircraft is in energy state and location along the approach would have helped prevent this issue. Additionally once it became clear that we were in an undesired configuration and energy state a discontinued approach should have been executed and a second attempt should have been made rather than trying to fix the situation.
Source: NASA Aviation Safety Reporting System (public domain). Reports are voluntary submissions and are not verified by NASA.