Air carrier crew reported a GPWS Obstacle warning and a slow speed condition while descending rapidly on a visual approach after improperly programming the aircraft automation. The crew regained aircraft control and returned to stable flight.
Synopsis
Air carrier crew reported a GPWS Obstacle warning and a slow speed condition while descending rapidly on a visual approach after improperly programming the aircraft automation. The crew regained aircraft control and returned to stable flight.
Narrative
While descending on a visual approach to RWY 13R at SAT; the FO felt he was too high while on base leg. I'm not sure why; but he decided to turn the autopilot off right before intercepting final. He was descending at what I thought was too high a rate and I told him he was going to be too low if he keeps descending at the current rate this far out. He had set 2200' in the altitude window which was the FAF altitude. Right before turning final he kept descending. It continued to appear to me that he was going to get too low and I instructed him to start leveling off. It was at that time we got a caution obstacle"; I re-instructed him to not descend. I looked outside and could see a tower that we were clear of which I believed to be the reason for GPWS alert. As I turned my attention back inside I realized we are starting to get too slow; I reached up pulled speed and announced the slow speed condition. He then stowed the speed brakes and the aircraft started accelerating back to the selected speed.We both failed to recognize that the Flight Directors were not selected off which did not force the aircraft into the Autothrust SPEED mode.When the autopilot was disconnected during a time compressed portion of the approach; I believe this was done as a result of the FO's perception of his belief of being too high.During the numerous distractions occurring at that point; I failed to recognize the Flight Directors were not off; which would have forced the Autothrust into SPEED mode.I understand the importance of getting the aircraft into SPEED mode when the flight directors are not going to be followed. In this instance; this was clearly an oversight on my part. As a way to personally limit this happening going forward; I intend to avoid any hand flown visual approaches; as much as feasible.This event unfolded very quickly. I have spend numerous hours replaying what occurred and have thought about the severity of the situation. I fully intend to change my awareness to prevent such events from occurring again."
Second reporter narrative
Arriving in the vicinity of the SAT airport we accepted a visual approach for Runway 13R. I selected 2200ft to assist in beginning the visual approach. I selected the gear down flaps two configuration to set up for the straight in portion of our visual approach. My first mistake occurred when I decided to turn the autopilot off with the speed brakes deployed and use open descent to reach the desired altitude. I was aware the flight directors also needed to be turned off as I would not be following them(this did not occur). This configuration resulted in the aircraft slowing to an undesired speed. The captain an I discussed both the aircraft speed and altitude; and I mentioned the flight directors. At that point the first distraction occurred when the GPWS announced Obsticle" because of our position and rate of descent. At this time I advanced the thrust levers as the captain selected a greater speed on the flight guidance panel. About this time the aircraft announced "speed speed". As the trust advanced I realized my oversight of the speed brakes being deployed. I retracted the speed brakes and we were then able to accelerate and resume stable flight. I did not realize I still had the speed brakes deployed upon level off. Also my disconnecting of the autopilot caused a greater workload for the crew; distraction added with our rate of descent triggering the "Obsticle" callout. Recomendation: As we observed the aircraft approaching an undesired state we should have leveled off and accelerated much sooner while abandoning the visual approach. Requesting a delay vector would have provided time to descend to my desired altitude to begin the straight in approach with no change in the level of automation being used."
Source: NASA Aviation Safety Reporting System (public domain). Reports are voluntary submissions and are not verified by NASA.