AIRWORTHINESS DIRECTIVE

For the reasons set out in the background section, the CASA delegate whose signature appears below issues the following Airworthiness Directive (AD) under subregulation 39.1 (1) of CAR 1998. The AD requires that the action set out in the requirement section (being action that the delegate considers necessary to correct the unsafe condition) be taken in relation to the aircraft or aeronautical product mentioned in the applicability section: (a) in the circumstances mentioned in the requirement section; and (b) in accordance with the instructions set out in the requirement section; and (c) at the time mentioned in the compliance section.

Boeing 737 Series Aeroplanes

AD/B737/187 Captain’s Pitot Heater 9/2002

Applicability: Model 737-600, -700, -800, and -900 series aeroplanes listed in Boeing Alert Service Bulletin (ASB) 737-24A1150, dated 11April 2002.

Requirement: 1. Measure the electrical voltage at the circuit breaker for the aircraft captain's pitot heater to determine if the pitot heater is connected to the correct power supply bus, in accordance with ASB 737-24A1150. If the measurement is 100 to 122 volts alternating current (AC), no further action is required by this Directive.

2. If the measurement is not 100 to 122 volts AC, perform all actions associated with connecting the subject circuit breaker wire to the 115-volt AC standby power supply bus (including performing a test to ensure that the pitot heater system operates correctly, repeating the measurement of the electrical voltage at the circuit breaker for the captain's pitot heater, and troubleshooting and correcting the wire connections until the test and measurement are successful), in accordance with ASB 737-24A1150.

Note: FAA AD 2002-14-20 Amdt 39-12820 refers.

Compliance: For Requirement 1 - Within 60 days after the effective date of this Directive.

For Requirement 2 - Before further flight after the Requirement 1 voltage measurement.

This Airworthiness Directive becomes effective on 5 September 2002.

Boeing 737 Series Aeroplanes

AD/B737/187 (continued)

Background: This Directive requires measurement of the electrical voltage at the circuit breaker for the aircraft captain’s pitot heater to determine if the pitot heater is connected to the correct power supply bus and, if necessary, the performance of corrective action.

These actions are necessary to prevent ice from blocking the pitot tube that provides airspeed data to the captain. Such ice blockage could lead to the flight crew receiving incorrect airspeed data, which could result in loss of control of the aeroplane if the flight crew fails to recognize that the data are incorrect.

Eugene Paul Holzapfel

Delegate of the Civil Aviation Safety Authority 29 July 2002

The above AD is notified in the Commonwealth of Australia Gazette on 14 August 2002.