AIRWORTHINESS DIRECTIVE

CAA-AD-024/2002

Date of issue: February 21, 2002

AIRCRAFT - ENGINES - HIGH PRESSURE OIL PUMP (ATA 79) - REPLACEMENT

Applicability: ATR 42-200, -300, and -320 model aircraft.

Effective date: April 18, 2002

Compliance: Required as indicated in DGAC AD 2002-071-091(B).

Remarks: The compliance of this AD must be recorded in Aircraft Logbook, where applicable the requirements of this AD must be integrated into Aircraft Technical Documentation. Address inquiries concerning this AD to: Civil Aviation Authority, Airworthiness Division, Ruzyne Airport, 160 08 Prague 6, Czech Republic, tel.: 420 2 33320922, fax: 420 2 20562270.

Ing. Pavel MATOUŠEK

Director of Airworthiness Division

CAA CZ

DGAC AD No.: 2002-072-064(B)

ATR

ATR 72 aircraft

Engines - High pressure oil pump - Pressure Regulating Valve (PRV) (ATA 79)

1. APPLICABILITY:

ATR 72-101, -102, -201, -202, -211, and -212 model aircraft.

2. REASONS:

During years 1999 and 2000, three cases of propeller pitch lock, during final approach, have been experienced on ATR fleet. During two of these events the asymmetric power resulting from the propeller pitch lock was not recognised by the crew during landing and the aircraft veered off the runway after selection of reverse power while the "Low Pitch" condition was not effective for both engines.

A first measure has been to provide operators with enhanced operational procedures associated with reverse application. This has led ATR to revise the Airplane Flight Manual to add instructions that prohibit the crew from selecting the reverse position on the engines in the event of propeller asymmetric power. This AFM revision was mandated by AD No. 2000-437-052(B).

Extensive investigations were performed on the suspected components of the propeller pitch control system lo isolate the root cause of the pitch lock issue. Performance anomalies were evidenced on two HP Oil pump.

Based on the test results, these HP Oil Pump anomalies, when independently considered, would not lead lo a propeller pitch lock. Nevertheless, the analysis of how the HP Oil Pump PRV fitted on the PW 124B/127 is interacting with the propeller control systems shows that this equipment could be a contributing factor lo a propeller pitch lock condition especially when associated with oil contamination.

The actions rendered mandatory by this Airworthiness Directive (AD) are intended lo modify pressure regulating valves (PRV) in order to avoid a propeller pitch lock situation and reduced controllability of the aircraft during landing.

3. ACTIONS:

The following measures are rendered mandatory from the effective date of this AD.

At the first opportunity and at the latest before June 30, 2004, replace all Pratt & Whitney Canada PW 124B and PW 127 HP Oil Pump PRV's by PRV modified in accordance with Pratt & Whitney Canada Service Bulletin 21570.

REF.: PRATT & WHITNEY CANADA Service Bulletin 21570.

EFFECTIVE DATE: FEBRUARY 02, 2002