Aurigny AT72 near Manchester on Mar 4th 2016, stab trim problems due to ice accretion

Last Update: February 9, 2017 / 15:43:26 GMT/Zulu time

Bookmark this article
Incident Facts

Date of incident
Mar 4, 2016


Flight number

Aircraft Registration

Aircraft Type
ATR ATR-72-200

ICAO Type Designator

An Aurigny Air Services Avions de Transport Regional ATR-72-212A, registration G-COBO performing flight GR-671 from Manchester,EN to Guernsey,CI (UK) with 27 passengers and 4 crew, was climbing out of Manchester when the crew stopped the climb at FL170 reporting pitch trim problems and decided to divert to East Midlands,EN (UK) for a safe landing about 20 minutes later.

The French BEA reported based on information from Britain's AAIB, that the occurrence was rated a serious incident and is being investigated by the AAIB.

On Mar 17th 2016 The Aviation Herald received information that company dispatch queried the crew on their previous leg inbound to Manchester whether they wanted to de-ice the aircraft while on the ground, the crew advised they would consider this while on the ground. On the ground the crew advised de-icing was not needed on two occasions although there was heavy snow fall. Soon after takeoff the crew notified company dispatch that they were diverting due to ice buildup on wings and stabilizer.

On Feb 9th 2017 the AAIB released their bulletin concluding the causes of the serious incident were:

The investigation concluded that ice contamination affected the tailplane and caused pitch control difficulty after the aircraft rotated, on departure. The evidence indicated that this would have been avoided if the aircraft had been de-iced/anti-iced and then inspected carefully before flight.

The crew considered, before parking, that de-icing was probably going to be unnecessary. It may then have become difficult for them to change their assessment because of ‘confirmation bias’, even though they were in freezing conditions and snow was falling. A contributory factor may have been the crew’s lack of experience operating aircraft in such conditions.

The commander optimistically thought that lying snow would blow off the aircraft before rotation; an assessment that was flawed and a possible reflection on the training the pilots had received for such winter conditions. The operator has recognised that recurrent winter training for pilots may have been over-reliant on self-study and has taken remedial action.

The AAIB reported the captain (58, ATPL, 8,276 hours total, 928 hours on type) was pilot flying. The captain experienced he needed less back-pressure to rotate the aircraft than expected, then maximum nose down trim was needed to maintain appropriate climb attitude while still exercising forward pressure on the control column. The autopilot was engaged but disconnected four times. After levelling off at cruise level the captain still needed to provide forward pressure on the control column and decided to divert to East Midlands. While descending the aircraft flew out of icing conditions and the control difficulties dissipated. The crew assessed that ice accretion had caused the control difficulties and performed a normal landing. No ice was found on the airframe after landing, the captain therefore assessed a mechanical problem had occurred and placed the aircraft unserviceable.

The AAIB wrote: "Neither the commander nor the operator immediately considered that a serious incident had occurred and there was a three day delay before the AAIB was notified. The AAIB then assessed the occurrence as one ‘which could have caused difficulties controlling the aircraft’ so, in accordance with Regulation (EU) No 996/2010, it was classified as a serious incident."

The AAIB reported the aircraft manufacturer analysed - based on the data read off the flight data recorder - that the aircraft's abnormal pitch up tendency was consistent with the aerodynamic effects of upper surface icing on the horizontal tail plane, the layer was estimated at 5mm of ice accreted on the upper surface of the elevator.

The AAIB analysed:

When flying the approach into Manchester in icing conditions, the crew saw little ice accreting on the aircraft. This may have led them to assume ice accretion was unlikely while on the ground. Also, the commander’s declaration of the temperature being a little above 0ºC may have reinforced this belief. He told the co-pilot the snow did not appear to be “sticking” and, before parking, he considered they could probably “get away without de-icing”.

The commander advised the co-pilot he would “have a good look” during his external inspection but his early pronouncement may have made both pilots susceptible to ‘confirmation bias’. From then on, they may have subconsciously tried to make the evidence available to them accord to the commander’s original assessment. This was apparent when the commander saw snow on other aircraft and declared it must have accumulated overnight. Neither pilot seemed to consider the possibility there might be unseen ice on the upper surfaces after landing, nor that the skin temperature would probably have been colder than 0ºC. The large quantity of fuel that was added might have caused the skin temperature of the wings to warm above 0ºC but the tailplane temperature would have remained at or below 0ºC.

Photographs taken on the ground at Manchester showed snow lying on the aircraft but the commander assessed it was not “sticking” and considered that any which remained would “blow off” during takeoff. He could not see all the upper surfaces and did not arrange a ‘contamination check’. However, even without such a check, it was apparent both ‘atmospheric icing conditions’ and ‘freezing conditions’ existed because the temperature was less than 3ºC, with visible moisture present. These were conditions in which the guidance is to de-ice/anti-ice an aircraft completely and check it afterwards. If the co-pilot had had previous experience of winter operations, he might have questioned the commander’s decision not to de-ice/anti-ice.

The decision to depart without being certain the aircraft was free of ice, suggests the crew were affected by ‘optimism bias’ and only foresaw a positive outcome ie any snow ‘blowing off’.

The AAIb continued analysis: "The manufacturer’s analysis was that the aircraft behaved in a manner consistent with the presence of ice contamination on the upper surface of the horizontal tailplane and the trim tab ran to the end of its nose-down travel while compensating. It was concluded that the autopilot was disengaged by its internal monitoring circuitry, as a result of the load experienced by the autopilot pitch servomotor, or a manual pitch input."

EGCC 041150Z 23004KT 0500 R23R/1200 +SN BKN001 00/M00 Q0988 RESN BECMG 1200 SN BKN002=
EGCC 041120Z 23005KT 0600 R23R/1200 +SN BKN002 00/M00 Q0988 RESN BECMG 1200 SN=
EGCC 041050Z 24006KT 1000 R23R/P1500 SN FEW002 BKN004 00/00 Q0988 NOSIG=
EGCC 041020Z 25008KT 2500 SN FEW002 BKN004 00/00 Q0988 NOSIG=
EGCC 040950Z 24007KT 1800 SN FEW002 BKN004 00/M00 Q0988 NOSIG=
EGCC 040920Z 24007KT 1200 R23R/P1500 R23L/P1500 SN FEW001 SCT003 BKN008 00/M00 Q0988 TEMP0 BKN003=
EGCC 040850Z 22006KT 1200 R23R/1400 R23L/P1500 SN FEW002 SCT004 BKN008 00/M00 Q0988 TEMPO 0600 SN BKN004=
EGCC 040820Z 24005KT 0800 R23R/P1500 R23L/P1500 SN FEW001 SCT003 BKN006 00/M00 Q0988 TEMPO 0600 SN BKN003=
EGCC 040750Z 23008KT 0600 R23R/1100 R23L/P1500 SN FEW002 SCT004 BKN008 00/M01 Q0988 TEMPO BKN002=
EGCC 040720Z 24007KT 0800 R23R/P1500 R23L/P1500 SN FEW004 SCT006 BKN010 01/M01 Q0988 BECMG BKN004=
EGCC 040650Z 25009KT 5000 -SNRA BKN012 02/M00 Q0988=
EGCC 040620Z 24009KT 7000 -SNRA FEW009 BKN015 02/M00 Q0988=
EGCC 040550Z 25011KT 9000 -RA OVC012 02/00 Q0988 TEMPO RA=
EGCC 040520Z 25011KT 9999 OVC030 02/00 Q0988 NOSIG=
Incident Facts

Date of incident
Mar 4, 2016


Flight number

Aircraft Registration

Aircraft Type
ATR ATR-72-200

ICAO Type Designator

This article is published under license from © of text by
Article source

You can read 2 more free articles without a subscription.

Subscribe now and continue reading without any limits!

Are you a subscriber? Login

Read unlimited articles and receive our daily update briefing. Gain better insights into what is happening in commercial aviation safety.

Send tip

Support AeroInside by sending a small tip amount.

Related articles

Newest articles

Subscribe today

Are you researching aviation incidents? Get access to AeroInside Insights, unlimited read access and receive the daily newsletter.

Pick your plan and subscribe


Blockaviation logo

A new way to document and demonstrate airworthiness compliance and aircraft value. Find out more.


ELITE Simulation Solutions is a leading global provider of Flight Simulation Training Devices, IFR training software as well as flight controls and related services. Find out more.

Blue Altitude Logo

Your regulation partner, specialists in aviation safety and compliance; providing training, auditing, and consultancy services. Find out more.

AeroInside Blog
Popular aircraft
Airbus A320
Boeing 737-800
Boeing 737-800 MAX
Popular airlines
American Airlines
Air Canada
British Airways