April 24, 1998 (date written)

October 15, 2001 (date revised)

TO: Turbo Products / Northstar Turbine Customers.

Gentlemen:

This letter has been written to answer questions about Northstar Turbine, Turbo Products FAA PMA parts, and interchangeability.

When we ran the engine certification test program in order to substantiate to the FAA the suitability of these FAA PMA parts; one topic of interest with the FAA was interchangeability. We substantiated to the FAA that these FAA PMA parts were interchangeable with the Pratt & Whitney Canada parts they replace, BOTH AS COMPLETE SETS AND INDIVIDUALLY.

IF there is a good reason to do so, (e.g. parts are needed to replace damaged parts in order to make a complete set); these FAA PMA parts may be intermixed with P&WC parts within an engine set. Examples:

1. T019551 PMA Nickel C.T. vanes may be intermixed with 3019551 P&WC Cobalt C.T. vanes.

2. T023401 PMA INCO 738 C.T. blades may be intermixed with 3023401 P&WC INCO 713LC C.T. blades. Etc.

Obviously, several comments are also appropriate:

1. If PMA and P&WC parts are to be intermixed; these two groups of parts should be distributed uniformly rather than grouped together. Example if Nickel and Cobalt vanes are mixed in the same engine, then the Nickel vanes should be distributed as uniformly around the vane assembly as possible and the Cobalt vanes should be distributed as uniformly around the vane assembly as possible.

2. Many of the durability advantages of the FAA PMA parts can not be fully realized. The FAA PMA blades and vanes are made from more durable nickel alloys and are coated with more durable Sermaloy J coatings. Example if PMA Nickel and P&WC Cobalt vanes are mixed in the same engine, then the hot section will need to be repaired (i.e. HSI) when the P&WC Cobalt vanes begin to become distressed. At that time the Cobalt vanes will need to be sent out for overhaul; while the Nickel vanes will be suitable for re-installation without any repair.

3. More than one PT6 repair facility has seen engine assemblies which have had a mixture of FAA PMA parts along with P&WC parts. Such a mixture, is in effect, an informal comparison test; which graphically illustrates the advantages of using the FAA PMA parts.

In conclusion, we believe that it is in the engine operator's best LONG TERM interest to install the FAA PMA parts in sets. However, we also acknowledge that economics play a part of everyone's decisions. For this reason, we can well understand why some one would be reluctant to replace COMPLETELY SERVICEABLE parts; just to be able to install a complete set of MATCHING parts.

If / when I can be of additional assistance, please call me at 781 828 0451, or FAX me at 781 821 4091.

Sincerely,

Ralph Hawkins

Chief Engineer

Northstar Turbine LLC