Manx2 L410 at Isle of Man on Nov 5th 2012, rejected takeoff after being airborne

Last Update: May 9, 2013 / 15:05:12 GMT/Zulu time

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Incident Facts

Date of incident
Nov 5, 2012

Classification
Report

Flight number
NM-116

Aircraft Registration
OK-ASA

Aircraft Type
Let L-410 Turbolet

ICAO Type Designator
L410

A Manx2/VanAir Let L-410, registration OK-ASA performing flight NM-116 from Isle of Man to Blackpool,EN (UK) with 10 passengers and 2 crew, was accelerating for takeoff from runway 26 with the captain (40, ATPL, 3,221 hours total, 2,827 hours on type) being pilot flying. Upon reaching Vr (81 knots) the captain initiated rotation when both flight crew heard a loud noise, the captain checked the engine instruments which showed no abnormal indication, there was no yaw and no abnormal aircraft behaviour, the aircraft had become airborne in the meantime. The captain retarded both power levers to idle, descended the aircraft back onto the runway for a touchdown close to the intersection with runway 03/21 and slowed the aircraft to taxi speed before the end of the runway. Maximum speed over ground was 101 knots. The aircraft vacated the runway at the end of runway 26, the noise was still present though at lower level. The aircraft taxied to the apron, was shut down, passengers disembarked normally. Another aircraft on approach was instructed to go-around, a runway inspection found no debris on the runway.

The United Kingdom's Air Accident Investigation Board (AAIB) released their bulletin into the serious incident releasing following summary:

The source of the noise heard by the crew during the takeoff was traced to damage in the gas generator and power turbine stages of the left engine, caused by a broken balance plug released from the centrifugal compressor disc. The damage sustained by the engine was not sufficient to cause a significant loss of power and therefore the usual cues for the flight crew of an engine failure, loss of power and associated yaw, were missing. The flight crew were also startled by the level of noise, as it was outside of any of their previous experience.

The commander suspected a failure of the left engine but was not certain as to what had happened. Realising that there was sufficient runway ahead to land the aircraft safely, he decided to close the power levers and abort the takeoff.

The AAIB reported that the flight data recorder was retrieved and downloaded, the data contained 76 but not the incident flight. The cockpit voice recorder did contain the incident flight, however the cockpit area microphone suffered a fault attenuating the recordings.

The day after the occurrence an inspection of the left hand engine revealed no external evidence of damage or leaks, however, when the propeller was turned manually a metallic rubbing noise was heard from the power turbine section of the engine. No other defects were identified. The left hand engine was removed from the aircraft and sent to the engine manufacturer for further analysis. The manufacturer identified a balance plug had broken and had been released from the centrifugal compressor disc. The plug had travelled along the gas path through the engine causing damage to the centrifugal compressor, the gas generator, power turbine nozzle guide vanes and turbine blades as well as 9 intermediate turbine temperature (ITT) thermocouples. The damage was insufficient to cause a significant loss of engine power. The balance plug had failed due to a fatigure crack that developed originating from the thread root of the plug's uppermost screw thread. The AAIB stated: "The engine manufacturer identified either insufficient assembly torque or ineffective securing of the plug after installation as possible causes for the balance plug becoming loose."
Incident Facts

Date of incident
Nov 5, 2012

Classification
Report

Flight number
NM-116

Aircraft Registration
OK-ASA

Aircraft Type
Let L-410 Turbolet

ICAO Type Designator
L410

This article is published under license from Avherald.com. © of text by Avherald.com.
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