AD/HS 125/179 UAM100 Current Limiters (Cth)

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 39.001(1) of CASR 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.

British Aerospace BAe 125 Series Aeroplanes

AD/HS 125/179 UAM100 Current Limiters 8/2006 DM

Applicability:	Model HS.125 series 700A and 700B aeroplanes, on which Raytheon Modification 252885 has been incorporated or British Aerospace 125 Service Bulletin SB 24-239-2885 has been accomplished.
All Model BAe.125 series 800A (including variants C-29A and U-125), 800B, 1000A and 1000B aeroplanes.
All Model Hawker 800 (including variant U-125A) and 1000 aeroplanes together with and Model Hawker 800XP aeroplanes, serial numbers 1 through 258768 inclusive.
Requirement:	1.    Measure the resistance of the applicable current limiters, part number (P/N) UAM100, in accordance with paragraph 3.A.(2) of the Accomplishment Instructions of Raytheon Service Bulletin SB 24-3793, dated May 2006.  The applicable current limiters are listed in Table 1 of the service bulletin.
A review of aeroplane maintenance records is acceptable in lieu of the Requirement 1 resistance measurement, if the following criteria can be determined conclusively from that review:
(1)   The records review determines conclusively the date of the most recent 24-month "F" or "F7" inspection, as applicable, of current limiters and the date of the most recent replacement of current limiters, and that the inspection and replacement were not accomplished between 1 February 2006 and the effective date of this Directive.
(2)   The records review determines conclusively the picking tag PO of the current limiters, and that the current limiters are not from picking tag PO 4501760749 or PO 4501743706.
2.    If the measured resistance of a current limiter is less than 0.46 milliohms or greater than 0.56 milliohms, replace the part with a new part in accordance with SB 24-3793.  The new part must not be from picking tag purchase order (PO) 4501760749 or PO 4501743706 and must be the correct resistance in the range of 0.46 milliohms to 0.56 milliohms.

3.    Submit the Service Bulletin/Kit Drawing Report Fax (attached to SB 24-3793) to the Manager, Hawker Model Group, Raytheon Aircraft Company, Product Support Department (211), P.O. Box 85, Wichita, Kansas 67201-0085; fax [phone].  The report must include the results of the Requirement 1 measurements (paragraph (f) of the corresponding FAA AD), the name(s) of the owner and operator of the aeroplane, the aeroplane registration number, the aeroplane serial number and the number of landings and flight hours on the aeroplane.
4.    Current limiter, P/N UAM100, may not be installed on any aeroplane as a replacement part unless the part meets one of the following criteria:
a.     The picking tag PO of the current limiter can be determined conclusively from a review of aeroplane maintenance records and shown not to be from picking tag PO 4501760749 or PO 4501743706.
b.    The resistance of the current limiter is measured and determined to be of the correct resistance in accordance with Requirement 1.
Note:  FAA AD 2006-12-20 Amdt 39-14646 refers.
Compliance:	For Requirement 1 - Either within 30 days or 25 hours time in service, whichever occurs first, after the effective date of this Directive.
For Requirement 2 - Before further flight after the Requirement 1 measurement.
For Requirement 3 -
If the measurements were accomplished after the effective date of this Directive - Within 10 days after the inspection.
If the measurements were accomplished before the effective date of this Directive - Within 10 days after the effective date of this Directive.
For Requirement 4 - As of the effective date of this Directive.
This Airworthiness Directive becomes effective on 3 July 2006.

Background:

The United States Federal Aviation Administration (FAA) has received several reports indicating that certain current limiters, P/N UAM100, have opened within two to four hours after installation.  The current limiters are the primary bus feed for the PE, PS1 and PS2 busses.  Three of the reports indicated that one or more of the current limiters opened in flight.  Investigation has revealed that the supplier provided parts that did not meet specification and that a specific batch of parts has exhibited the anomaly of opening.  The suspect current limiters were delivered beginning
1 February 2006 and have picking tag PO 4501760749 or PO 4501743706.  These suspect parts could be installed on any or all three busses.  Loss of all three busses may occur, resulting in loss of all primary direct current electrical power.  This condition, if not corrected, could result in the aeroplane operating only under emergency power.

This Directive requires measuring the resistance of the current limiters for the PE, PS1 and PS2 busses and, if necessary, replacing a current limiter with a new part. The Directive also requires reporting certain information to the aeroplane manufacturer. Additionally, the Directive allows a records review for determining if suspect current limiters were installed, which may exempt aeroplanes from the required measurement.

James Coyne
Delegate of the Civil Aviation Safety Authority

22 June 2006