Airworthiness Notices - B040, Edition 1 - 22 December 1997

Liquid Penetrant Inspection Requirements

Purpose

This Airworthiness Notice provides notification of Transport Canada policy regarding the use of liquid penetrant inspection (LPI) products for the examination of aircraft structures or components and will form the basis for proposed standards.

Background

LPI penetrants are available in three types: Type I Fluorescent, Type II Visible (color contrast) and Type III Visible and Fluorescent. The Type I products have sensitivity levels assigned to them, ranging from 1 (low) to 4 (ultrahigh). The Type II and Type III products generally do not have such levels assigned.

Different standards governing the use of LPI have been specified by manufacturers in the past. Some of these have permitted the use of Type II visible products for final inspection of aircraft products or components. The current standard ASTM E1417 replaces earlier standards and specifies Type I Fluorescent products for such inspections.

Fluorescent penetrant systems (high sensitivity) are significantly more likely to detect a fine defect before the part or component fails. To ensure that the most effective penetrant method is used for critical aviation components the minister herein advises that only fluorescent penetrant inspection systems classified as having the appropriate inspection sensitivity are recommended for final in-service inspection of aircraft structures or components.

Note:  Residue from color contrast materials, introduced by inspections carried out previously, may create contamination of the fluorescent penetrant process, causing poor inspection results.  To ensure optimum inspection results are achieved it is essential to thoroughly remove visible dye inspection residue by pre-cleaning the part using approved cleaning methods.

References

ASTM  E1417 “Standard Practice for Liquid Penetrant Examination”.

Recommended Practice for Canadian Maintainers

For penetrant inspections, only Type l  Fluorescent products are recommended. ASTM E1417 is the standard which applies.

Where manufacturers' recommendations specify  products other than Type l, or specify standards other than ASTM E1417 the substitution of  a Type l product is recommended. 

Expiration Date

This notice will be canceled following the introduction of its contents as an instruction in the Canadian Aviation Regulations as an appendix to Standard 571.

For Minister of Transport

D.B. Sherritt
Director, Aircraft Maintenance
and Manufacturing