Editors' Choice: Comair crew prevailed in Brasilia icing stall

 - May 28, 2008, 7:13 AM

What was to have been a routine milk run on March 19 from Nassau, Bahamas, to Orlando, Fla., for Comair Flight 5054 turned into several moments of sheer terror when the Embraer EMB-120 Brasilia began accruing a coating of ice as it entered IMC at 18,000 ft about 46 min after takeoff.

As the windshield began to ice over, the crew of the twin turboprop activated the ice protection system and it began to clear. But the first officer soon discovered that the de-icing boots on the right wing and the spinner on the right prop were also accumulating a layer of ice that extended farther back than he had ever seen previously.

After cranking up the ice protection systems to high, the FO warned the captain the airspeed had dropped to 160 kt from 175 kt as the airplane  exhibited a need for nose-up trim. The flight data recorder (FDR) showed that the airspeed continued to decrease to about 140 kt while the trim requirement escalated to nearly full nose-up.

In response to the rapidly decreasing airspeed, the captain disconnected the autopilot, added power and pushed the nose over to try to recover speed. Despite this prescribed icing stall recovery technique, the Brasilia’s speed continued to deteriorate until it reached 130 kt.  

At this point, the airplane began oscillating about its pitch, roll and yaw axes, rolled over sharply to the right and descended steeply at least 7,000 ft into VMC, where the crew was able to recover. The captain told National Transportation Safety Board (NTSB) investigators that the electronic attitude display indicators “presented no useful information” during the descent.

Examination of the FDR showed that the Brasilia rolled roughly 90 deg left, then back to near level. In the next 24 sec, it rolled about 110 deg left, back to level, 120 deg right, back to level and then 360 deg to the right and back to nearly level. During the wild descent, the aircraft reached speeds of 240 kt and a vertical acceleration of +3.6 g.

Flight 5054 finally broke out between cloud layers at about 10,000 ft, where the pilots were able to regain control and halt the descent. Although the Embraer handled normally after the recovery and its systems indicators showed nothing unusual, the pilots elected to make a precautionary landing at West Palm Beach (Fla.) Airport about 12 min after the start of the upset.

Further examination revealed that the aircraft sustained substantial damage to its elevators and horizontal stabilizer. However, none of the 25 passengers or crew suffered injuries during the incident.

The NTSB has not completed its investigation of the stall and rollover, but it was expecting to issue a package of recommendations shortly. There have been at least six other incidents and one fatal accident involving EMB-120s that experienced significant losses of airspeed after encountering unexpected icing conditions.