AD/Aircon/14 Zonal Drying System Regeneration Air Duct Overheat (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.

Airconditioning Equipment

AD/AIRCON/14 Zonal Drying System Regeneration
Air Duct Overheat 7/2006 TX

Applicability:

All airplanes equipped with German LBA Supplemental Type Certificates (STC) TA0733, TA0259, LBA.21E2.TA0609, LBA.21E2.TA0270, LBA.21E2.TA0307 or LBA.21E2.TA0636.

These STC’s provide for the installation of zonal dryer part numbers 3000-002,
1000-001 or 2001-006 manufactured by CTT Systems AB, Nykoping, Sweden.

These STC’s are installed on, but not limited to the following aircraft models:

Boeing 747-430;

Boeing 737-700;

Boeing 737-800;

Airbus A330-300;

Airbus A330-200; and

Bombardier CL600-2Bl9.

Requirement:

Switch off the zonal drying system and render the system inoperative by pulling and securing the appropriate circuit breaker in accordance with the related maintenance instructions.

Note 1:  EASA AD Number 2006-0118R1-E dated 15 May 2006 refers.

Note 2:  CTT Systems Information Letter No. IL06-01 and Lufthansa Technik Service Information Letter No. LHT 06-001 refer.

Compliance:

Before further flight after the effective date of this Airworthiness Directive.

This Airworthiness Directive becomes effective on 19 May 2006.

Background: One incident has been reported where the regeneration air ducting downstream of a zonal dryer P/N 3000-002, installed in a Boeing B747-400 aircraft, showed signs of premature material failure.  The problem is probably caused by high regeneration air temperature.  The zonal dryer’s normal safety protection devices should have prevented the regeneration air temperature from rising above 80^o C.  It is yet to be determined why this function did not work properly.

David Villiers
Delegate of the Civil Aviation Safety Authority

17 May 2006