Expressjet E145 at Moline on Aug 29th 2011, runway excursion
Last Update: May 20, 2016 / 11:35:31 GMT/Zulu time
Incident Facts
Date of incident
Aug 29, 2011
Classification
Incident
Cause
Runway excursion
Airline
Expressjet
Flight number
XE-5821
Departure
Denver, United States
Destination
Moline, United States
Aircraft Registration
N27152
Aircraft Type
Embraer ERJ-145
ICAO Type Designator
E145
Airport ICAO Code
KMLI
The runway was closed for about 2 hours until the aircraft was moved back onto paved surface and off the runway.
The airline confirmed the aircraft veered off the runway and said they are working with the NTSB to determine the causes of the occurrence.
On May 20th 2016 the NTSB released their final report concluding the probable cause of the incident was:
The uncommanded left deflection of the airplane's nose wheel likely due to seal deterioration and subsequent contamination within the Electrohydraulic Servo Valve (EHSV). Contributing to the incident was the undersized condition of the filter plugs within the EHSV which likely caused the C2 orifice filter seal to extrude and deteriorate.
The NTSB summarized crew statements, that the flight was uneventful until the nose gear touched down. After the nose wheels touched down the aircraft veered left, the crew used right rudder and right differential braking, however, as the aircraft slowed through 90 knots it began to turn hard left, departed the left side of the runway, assumed a heading parallel to the runway briefly and continued to turn coming to a stop at a magnetic heading of 076 degrees. During the runway excursion the aircraft collided with a runway sign and crossed taxiway E. Both pilots reported pressing the nose wheel steering disengage button during the roll out.
Tests of the various aircraft systems including brakes and nose wheel steering found no fault at first tests. The nose wheel steering reacted normally to steering inputs as well as the steering disengage button. However, during enhanced tests the NTSB discovered "that the flow rate through the bypass valve when the valve was open was much lower than required. When the manifold was disassembled, a flat piece of clear plastic was discovered on the bypass valve "C2" filter screen. The bypass valve opens when the steering system is disengaged. It connects the two steering actuating cylinder hydraulic chambers and allows the nose wheel to free caster."
During further tests "the EHSV, P/N 22253282-103, S/N 278A, was removed from the Steering Manifold Assembly and functionally tested per the manufacturer's Acceptance Test Procedure. The unit passed all sections of the acceptance test. Following the functional test the EHSV was disassembled. The C1 orifice filter seal exhibited a small area of material deformation and a small area of partial material separation. The outside diameter of the C2 orifice filter seal exhibited an area of missing material. These seals are located within hydraulic chambers that terminate at the C1 or C2 nozzles. If a nozzle becomes blocked, pressure can build within the C1 or C2 chamber, causing the control spool to move and therefore commanding the nose wheel to turn. The void that remained on the seal from the missing fragment of material was larger than the nozzle orifice."
The NTSB reported: "Embraer issued Service Bulletin (SB) 145-32-0099 (current revision 03, dated April 8, 2005) to address premature deterioration of O-ring seals within the EHSV. The bulletin states: "Instances of aircraft uncommanded swerving on the ground have been reported and in three of them a failure in the Nose Wheel Steering Hydraulic Manifold Electro Hydraulic Servovalve (EHSV) has been confirmed. In all cases, the Nose Wheel Steering system did not respond to steering commands in the cockpit. The manifold failures have been traced back to a premature deterioration of an O-ring in the electro-hydraulic servovalve (EHSV), which converts the electrical steering command into hydraulic pressure." The SB requires that the manifold assembly be fitted with an EHSV that has been screened and meets the requirements of HR Textron document DV1719. This document calls out critical dimensional requirements, including specific dimensions for the filter plug outer diameters. An "A" suffix is applied to the end of the valve serial numbers that have been screened and meet the requirements of this document. The incident EHSV serial number was stamped with the "A" suffix."
Metars:
KMLI 291852Z 15007KT 10SM CLR 26/14 A3004 RMK AO2 SLP170 T02560139
KMLI 291752Z 00000KT 10SM CLR 24/13 A3005 RMK AO2 SLP172 T02440128 10244 20144 58003
KMLI 291652Z 10003KT 10SM CLR 24/13 A3006 RMK AO2 SLP178 T02390133
KMLI 291552Z VRB03KT 10SM CLR 24/14 A3007 RMK AO2 SLP180 T02390144
KMLI 291452Z 08005KT 10SM CLR 22/14 A3006 RMK AO2 SLP176 T02170144 51007
Incident Facts
Date of incident
Aug 29, 2011
Classification
Incident
Cause
Runway excursion
Airline
Expressjet
Flight number
XE-5821
Departure
Denver, United States
Destination
Moline, United States
Aircraft Registration
N27152
Aircraft Type
Embraer ERJ-145
ICAO Type Designator
E145
Airport ICAO Code
KMLI
This article is published under license from Avherald.com. © of text by Avherald.com.
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