Introduction
On 11 January 2007, at approximately 0755 UTC, a Jetstream 4100 (registration G-MAJE, year of manufacture 1992) experienced a transient loss of power on its right engine during descent. The aircraft was operating a scheduled commercial passenger flight from Leeds Bradford Airport to Southampton Airport. There were 3 crew and 17 passengers on board; no injuries or damage were reported.
Flight History
The crew reported for duty at 0610 hrs. Due to strong winds, extra fuel was carried. The engine anti-icing, continuous ignition, and propeller de-icing systems were selected ON as per standard operating procedures. During the climb to FL190, the aircraft encountered moderate turbulence up to FL150 and light-to-moderate airframe icing. Ice shedding from the propellers was audible. In the descent, ice accretion was noted on the propeller spinners, extending rearwards approximately four inches.
At FL75, while entering cloud tops, the crew heard what they believed to be both engines running down. Power levers were near flight idle. The autopilot was engaged and no yaw was initially observed. Both torque indicators appeared at zero, and the right propeller speed had decreased. After a brief discussion, the crew transmitted a 'MAYDAY' call, suspecting double engine failure. The PF advanced the power levers, causing the aircraft to yaw right. He disconnected the autopilot, corrected the yaw, and levelled at FL70. The left engine was confirmed to be operating normally, and the call was downgraded to 'PAN'. Shortly thereafter, the right engine restarted spontaneously. After matching torque, the autopilot was re-engaged and the 'PAN' call cancelled. The aircraft completed an ILS approach to Runway 20 at Southampton and landed normally, met by the airport Rescue and Fire Fighting Service.
Weather
The synoptic situation featured a deep depression near Iceland with gale-force westerly flow over the British Isles. Frontal cloud with rain moved across southern England. Cloud layers from 1,500 ft to 12,000 ft with further layers above 15,000 ft were present. A radio-sonde ascent near the incident location recorded temperatures of -5.2°C at 10,000 ft, -3.2°C at 9,000 ft, -1.5°C at 8,000 ft, and +0.7°C at 7,000 ft.
Flight Recorder Data
The Solid State Flight Data Recorder and Cockpit Voice Recorder captured the event. At 8,000 ft, torque on both engines was reduced from 40% to about 10%, initiating a descent of 1,500 ft/min with a total air temperature of +8.5°C. Passing 7,500 ft, right engine speed began to decrease and its torque dropped to 0%. The crew remarked on the torque loss and subsequently transmitted a 'Mayday'. The right engine speed decreased to 25%, then 73 seconds later increased back to 100%; torque recovered to 44% and then matched the left engine at 40%. Left engine speed remained at 100% throughout.
Engineering Examination
Post-incident examination of the engines and anti-icing systems found no technical defects. Ground tests to full power were normal, and the aircraft was returned to service. Both engines were fitted with the original standard of air intake. The manufacturer noted that under certain icing conditions, ice can accumulate between the intake upper lip and the spinner, potentially leading to ice ingestion. A later intake design exists but is not mandated for the Jetstream 4100.