ATA SYSTEM: 21

REF: SIL 1
TO: Airbus A318/A319/A320/A321/A330/A340
TITLE: AIR CONDITIONING—OZONE CONVERTER MAINTENANCE

1.0 Effectivity:

2.0 Description:
This letter describes the procedure for return of the ozone converter to the original manufacturer, Engelhard Corporation, and the procedure for determining if the ozone converter efficiency is adequate to maintain the ozone concentration in the cabin below the levels specified in FAR 121.578.

2.1 Procedure for Return of Converter to Engelhard:
The ozone converter must be returned to Engelhard for testing as stated in the Abbreviated Component Maintenance Manual.
Maintenance such as cleaning should be done only by Engelhard because the use of improper cleaning techniques or chemicals can permanently deactivate the catalyst and/or damage the core.
In addition, disassembly and assembly should be done only by Engelhard because of the requirement to maintain the proper fit between the internal parts. Improper assembly can result in failure of the internal parts.

2.2 Calculations to Determine Compliance to FAR 121.578:
The calculation is the same for all of the aircraft listed in 1.0 Effectivity.
Three calculations are required. The ratio of cabin pressure (P) to sea level pressure(Po) must be calculated. Then, one must determine the efficiency necessary to ensure that the maximum cabin ozone concentration is below 0.25 ppmv and, in addition, must show that the time weighted average of 0.1 ppmv is not exceeded for each flight segment that exceeds 4 hours.

The aircraft manufacturer has recommended that the following value be used for the retention ratio(R):
R=0.34 (34% of the ambient ozone enters the cabin)

The following example assume that operator X wishes to use an A320 aircraft on a six hour route in the eastern North American region, where the expected cruise altitude will be 40000 feet. The take off altitude will be 5000 feet. The numbers used in the calculation are for example only. The operator should consult the FAR and determine the numbers to be used for the flight route.

The aircraft manufacturer has determined the ratio of cabin pressure(P) to sea level pressure(Po) is to be calculated using the cabin pressure, ambient pressure, and take off altitude shown in TABLE 1. The following is an example of the calculation of P/Po.

Refer to TABLE 1. For an expected cruise altitude of 40000 feet and a take off altitude of 5000 feet, the cabin pressure will be 10.85 psi.
P/Po=10.85/14.696=.739

The following example calculation shows the converter efficiency necessary to limit the cabin ozone concentration to a maximum of 0.25 ppmv in the A320.

At flight level 400, the maximum ozone concentration at an 84% confidence level is found to be 1.15 ppmv(OZ16) during February at 80 degrees north latitude in the eastern North American region. This ozone concentration is obtained from AC 120 38, page 15.

Minimum required converter efficiency:
=(1 [0.25/(OZ16)(R)(P/Po)])100
=(1 [0.25/(1.15)(.34)(.739)])100
=13%

The following calculation shows the converter efficiency necessary to limit the time weighted average ozone concentration to 0.1 ppmv.

Assume total flight segment time(Tfs) is 6 hours and flight level is 400.

Minimum required converter efficiency:
={1 [(0.1)(Tfs)/(OZ16)(R)(P/Po)(Tfs 1)]}100
={1 [(0.1)(6)/(1.15)(.34)(.739)(5)]}100
=58%

In this example calculation, the minimum required converter efficiency must be the highest of the two above calculated cases, that is, 58%. Thus, if the converter test efficiency is 49%, for example, the converter must be repaired or scrapped.

There are additional examples in the FAR if the operator wishes to use other conditions regarding ambient ozone concentration, flight time, and/or flight level.

After the efficiency has been determined by testing at Engelhard, the operator can determine how much longer the converter can be installed on the aircraft. The reduction in efficiency is estimated to be 0.003%/flight hour.

An example is given below to show how this information can be used to predict how much longer a converter can be used.
Assume: 76% Test efficiency
58% Minimum required efficiency

Remaining flight hours=(76 58)/0.003 = 6,000 flight hours

The above calculation is only an estimate. We recommend that a converter be returned to Engelhard for testing at the recommended flight hour duration published in the Airbus Industrie Maintenance Planning Document. This will assist the operator and Engelhard in developing more accurate predictions of efficiency vs. flight hours.

TABLE 1
CABIN PRESSURE
dependence on
AMBIENT PRESSURE AND TAKE OFF ALTITUDE

3.0 Identification:
Not Applicable

4.0 Action:
Return the converter to:
Engelhard Corporation
9800 Kellner Road
Huntsville, AL 35824

Attn: Ozone Converter Repair Station

For additional Information, contact Engelhard customer service at:
Telephone: 256-464-6333
Fax: 256-464-6344

5. Cost:
Contact customer service.

6. Reference:
Engelhard ACMM 21-11-04
Engelhard ACMM 21-11-05

7. Other Publications Affected:
Not Applicable.