AD 59-17-02

59-17-02 BOEING: Applies to all Model 707 Series Aircraft.

Compliance required as indicated.

Several reports have been received concerning the complete or partial disintegration of certain type Purolator, P/N 57737-2 filter elements used in pressure filter assembly BAC P/N F- 18C-12 (Purolator P/N 57726) and in auxiliary return filter, BAC P/N 10-3333-1 (Purolator P/N 64088).

There are two types of filter elements in use having the same P/N 57737-2. They are easily distinguishable by their design. One has a concave bottom plate and the other one a flat bottom together with nonmetallic mesh on the inner surface of the paper convolutions. Investigation has shown that the filter elements which disintegrated were of Purolator concave bottom type supplied prior to July 25, 1959.

Although all P/N 57737-2 concave bottom type filter elements may not be unsatisfactory, the number and location of unsatisfactory elements is unknown. Accordingly, to eliminate the existent adverse situation, the following must be accomplished.

(a) All present inventories of the concave bottom type Purolator filter elements P/N 57737-2 supplied prior to July 25, 1959, must be rejected for any further use in any type certificated aircraft.

(b) Replacement filter elements in the above noted pressure filter assembly or auxiliary return filter assembly shall utilize either the flat bottom type filter element, P/N 57737-2, or the concave bottom type P/N 57737-2 obtained from Purolator, and dated after July 25, 1959, or other approved replacement filter elements such as Aircraft Porous Media, Inc., P/N ACS-1790E- 12 or Bendix Filter Division, P/N 574615.

(Boeing service message dated July 23, 1959, also covers this subject.)