United Airlines Flight 1722

United flight 1722 lost altitude about 1 minute after departure while in instrument meteorological conditions, which included heavy rain. The airplane descended from 2,100 ft to about 748 ft above the water before the crew recovered from the descent. No injuries were reported, and the airplane was not damaged. The NTSB was not originally notified of the event, since it did not meet the requirements of Title 49 Code of Federal Regulations Part 830.5. However, the NTSB learned of the event about 2 months later and chose to open an investigation. By that time, both the cockpit voice and flight data recorder durations had been exceeded. The investigation utilized flight crew statements and other records as information sources.

The captain (who was the pilot flying) reported that he and the first officer had initially planned for a flaps-20 takeoff (flap setting of 20°) with a reduced-thrust setting, based on performance calculations. However, during taxi, the ground controller advised them that low-level windshear advisories were in effect. Based on this information, the captain chose a flaps-20 maximum thrust takeoff instead. He hand-flew the takeoff, with the auto throttles engaged. During the takeoff, the rotation and initial climb were normal; however, as the airplane continued to climb, the flight crew noted airspeed fluctuations as the airplane encountered turbulence. When the airplane reached the acceleration altitude, the captain reduced the pitch attitude slightly and called for the flap setting to be reduced to flaps 5. According to the first officer, he thought that he heard the captain announce flaps 15, which the first officer selected before contacting the departure controller and discussing the weather conditions. The captain noticed that the maximum operating speed indicator moved to a lower value than expected, and the airspeed began to accelerate rapidly.

The captain reduced the engine thrust manually, overriding the auto throttle servos, to avoid a flap overspeed and began to diagnose the flap condition. He noticed that the flap indicator was showing 15°, and he again called for flaps 5, and he confirmed that the first officer moved the flap handle to the 5° position.

The first officer stated that he “knew the captain was having difficulty with airspeed control”, and he queried the captain about it as he considered if his own (right side) instrumentation may have been in error. He did not receive an immediate response from the captain. Both pilots recalled that, about this time, the airplane’s pitch attitude was decreasing, and the airspeed was increasing. The first officer recalled that that the captain asked for flaps 1 soon after he had called for flaps 5, and when the first officer set the flaps to 1°, he then noticed the airspeed had increased further, and the control column moved forward.

Both pilots recalled hearing the initial warnings from the ground proximity warning system (GPWS), and the first officer recalled announcing “pull up pull up” along with those initial GPWS warnings. The captain then pulled aft on the control column, initially reduced power to reduce airspeed, and then applied full power to “begin the full CFIT [controlled flight into terrain] recovery.” The first officer recalled that, as the captain was performing the recovery, the GPWS alerted again as the descent began to reverse trend; data showed this occurred about 748 ft above the water. After noting a positive rate of climb, the captain lowered the nose to resume a normal profile, ensured that the flaps and speed brakes were fully retracted, and engaged the autopilot. The remainder of the flight was uneventful.

Figure 1 shows a perspective view of the flight track.

Figure 1- Flight Track with Annotations As a result of the event, United Airlines modified one of their operations training modules to address this occurrence and issued an awareness campaign about flight path management at their training center.

Verbatim NTSB analysis and probable cause from the NTSB dataset