Ryanair B738 at Liverpool on Jan 9th 2016, unreliable airspeed

Last Update: August 11, 2016 / 16:53:34 GMT/Zulu time

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Incident Facts

Date of incident
Jan 9, 2016

Classification
Report

Airline
Ryanair

Flight number
FR-9887

Departure
Alicante, Spain

Destination
Liverpool, United Kingdom

Aircraft Registration
EI-DWS

Aircraft Type
Boeing 737-800

ICAO Type Designator
B738

A Ryanair Boeing 737-800, registration EI-DWS performing flight FR-9887 from Alicante,SP (Spain) to Liverpool,EN (UK) with 173 passengers and 6 crew, was descending through FL110 towards Liverpool in instrument meteorological conditions in icing conditions with a total air temperature of +8 degrees C, when the captain's (41, ATPL, 12,000 hours total, 8,700 hours on type), pilot monitoring, indicated airspeed and indicated altitude data became erratic following an ALTN indication for the electronic engine control. The standby instruments and the first officer's instrument continued to remain in agreement. The first officer, pilot flying, had engaged autopilot B and autothrust. Following the ALTN indication the crew observed erratic thrust commands, hence the crew disengaged autothrust and used manual thrust for the remainder of the flight. The checklists for "unreliable airspeed" and "engine ALTN" were worked and the crew confirmed the first officer's instruments remained reliable data sources. The aircraft continued the descent and entered a hold at FL070 doing two turns in the holding pattern before leaving the hold for an ILS approach to Liverpool's runway 09. Shortly after leaving the hold the captain's instruments recovered and there were no further abnomal indications. The aircraft continued for a safe landing.

The AAIB released their bulletin concluding the probable cause of the occurrence was:

The erroneous airspeed and altitude indication was likely to have been caused by partial and transient ice blockage of the commander’s pitot probe whilst in light to moderate icing conditions. This was as a result of the failure of the pitot probe heating element. The partial icing conclusion is supported by the fact that the blockage alleviated itself in the descent when the IAS and ALT information returned to normal.

The AAIB analysed:

During the incident the commander noted that the symptoms appeared to indicate some form of blockage or restriction to his pitot probe thereby corrupting pitot information into the air data system. Icing was considered the plausible cause given the atmospheric conditions.

Although the airspeed and altitude information was unreliable, there was not a complete loss of information which suggests only a partial blockage of the probe which alleviated as the aircraft continued its descent.

Subsequent fault diagnosis carried out by the operator found that the commander’s (left side) pitot probe heater element had shorted to its casing. The item was replaced and the aircraft returned to service. The probe, Part No 0851HT, had accrued 17,864 hours and 10,385 cycles.

During this incident, as with previous similar events, there was no indication of pitot probe malfunction on the window/pitot heat panel. The aircraft manufacturer had issued Service Bulletin (SB) 737-30-1070 in April 2014 which introduced a minor modification to the pitot probe heater wiring. The modification ensures that in the event of a pitot heater malfunction, a master caution will appear in the cockpit. The SB compliance is at the Operator’s discretion and in this case the Operator had scheduled it for this aircraft’s next deep maintenance package.
Aircraft Registration Data
Registration mark
EI-DWS
Country of Registration
Ireland
Date of Registration
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Manufacturer
THE BOEING COMPANY
Aircraft Model / Type
BOEING 737-8AS
ICAO Aircraft Type
B738
Year of Manufacture
Fjld Subscribe to unlock
Serial Number
fAbj Subscribe to unlock
Maximum Take off Mass (MTOM) [kg]
cfej Subscribe to unlock
Engine Count
G Subscribe to unlock
Engine
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Main Owner
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Incident Facts

Date of incident
Jan 9, 2016

Classification
Report

Airline
Ryanair

Flight number
FR-9887

Departure
Alicante, Spain

Destination
Liverpool, United Kingdom

Aircraft Registration
EI-DWS

Aircraft Type
Boeing 737-800

ICAO Type Designator
B738

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