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Race Engine Technology Magazine

Document Number 260002

REVISION HISTORY

1.0 ABSTRACT

This document specifies the required procedures to be followed with regard to any EPI aircraft engine or PSRU involved in a propeller strike or sudden stoppage event. The requirements specified herein are similar to those specified by Lycoming (SB 533-A), Continental (SB96-11), Woodward Prop Governors (SB 33574B), McCauley Prop Governors (SB 215B), and the Slick Magneto Overhaul Manual (Page 4-1) for their respective aircraft products following a prop strike or sudden stoppage event.

2.0 DEFINITIONS

The following definition of PROPELLER STRIKE is taken from a blending of the requirements stated in Lycoming Service Bulletin SB 533-A, Continental Service Bulletin SB96-11, and AD-2004-10-14.

A propeller strike is defined as follows:

1. Any incident, whether or not the engine is operating, that requires repair to the propeller other than minor dressing of the blades; OR
2. Any incident during engine operation in which the propeller impacts a solid object which causes a drop in RPM and also requires structural repair of the propeller (incidents requiring only paint touch-up are not included). This is not restricted to propeller strikes against the ground, and although the propeller may continue to rotate, damage to the engine may result, possibly progressing to engine failure; OR
3. A sudden RPM drop while impacting water, tall grass, or similar non-solid medium, where propeller damage is not normally incurred; OR
4. Any propeller strike occurring at taxi speeds and during touch-and-go operations, involving any propeller tip-to-ground contact; OR
5. Any situation where an aircraft is stationary and the landing gear collapses causing one or more propeller blades to be bent or substantially damaged, or where a hangar door (or other object) strikes the propeller blade. These cases should be handled as a sudden engine stoppage because of potentially severe side loadings on the propshaft flange, propshaft bearings, and propshaft seal.

Whereas the definitions stated above are intended to be unambiguous, the reality of aircraft ownership is that those definitions are likely to become the genesis of endless quibbling about such arcane trivia as:

• How sudden is "sudden",
• How tall is tall grass?
• How deep does the water have to be?
• How much of an RPM drop? (50 RPM, 500 RPM) ?
  {Were you really watching the tach when the prop hit?}

These arguments are specious and merely constitute an attempt to rationalize one's way out of doing the required inspections. AND, even though a large number of such inspections find no damage at all, the consequences of undiscovered prop strike damage can be quite grave.

(If you doubt the susceptibility to such damage, take a look sometime at the tiny dowel on the back of a Lycoming crankshaft, which locates and drives the entire set of accessory case gears.)

3.0 COMPLIANCE

Circumstances which surround accidents are many and varied. Therefore, the circumstances of the accident cannot, in EPI’s opinion, be used to predict the extent of the damage to the engine or the PSRU, or to assure the future reliability of either the engine or the PSRU.

3.1 Engines and PSRU’s

As the designer and manufacturer of the subject engines and / or PSRU’s, EPI, Inc. takes the position that in the case of a sudden engine stoppage, propeller strike, or the loss of a propeller blade or tip, that the affected engine(s) and/or PSRU(s) shall not be returned to service before being removed and returned to EPI, Inc. for a complete disassembly and inspection of:

1. all the rotating and reciprocating parts,
2. the accessory drive components,
3. any gear-driven devices or accessories installed on the engine or PSRU at the time of the incident (including, but not limited to: rotating fuel pumps, oil pressure and scavenge pumps, ignition distributors and/or magnetos, hydraulic pumps, vacuum pumps)
4. all propeller drive and governor drive components, bearings, seals and housings.

Any of the above parts which are covered by a manufacturer's document defining inspection after such incidents shall be inspected in accordance with the applicable documents.

Any parts not so covered are to be completely inspected for conformity to original design drawings with respect to concentricity, straightness and runout, followed by complete inspection by accepted NDT methodology and declared, as a result of those inspections, to be undamaged.

For ferromagnetic parts, the inspection standard is ASTM E-1444. For non-ferromagnetic parts, the inspection standard is ASTM E-1417.

3.2 Propeller Governors

In accordance with Woodward Prop Governor Service Bulletin 33574B and McCauley Prop Governor Service Bulletin 215B, EPI defines the following requirements with regard to the prop governor installed on the PSRU at the time of a prop strike or sudden stoppage incident.

The abnormally high loads imposed by a sudden stoppage or prop strike require that particularly close attention be given to the propeller governor rotating parts, in addition to meeting all other requirements of overhaul in accordance with the appropriate overhaul manuals. Therefore:

1. For the information of the overhauling agency, the governor must be tagged indicating that it was involved in such an incident;
2. The governor must be inspected and overhauled according to the Service Manual appropriate to the specific governor, paying particular attention to the following procedures:
        (1) MPI of the flyweight assembly components, idler gear and drive gear according to the appropriate manual;
        (2) Careful examination of all rotating parts for any signs of cracks or other damage.