Time for a Change?
There are two basic reasons for changing propellers:

  • To restore original performance compromised by wear and tear
  • To upgrade performance

Whether you are motivated by one or both reasons, changing propellers deserves your careful consideration. Your propeller is intimately linked to aircraft performance, operating in partnership with all other components.

Any number of factors can enhance or deter the performance you expect. With that in mind, we have prepared the following information to explain the available options.


Understanding Your Options
There are four basic ways to change propellers:

  • OEM Type Certificate
  • One-time Field Approval
  • Experimental Certificate
  • Supplemental Type Certificate

OEM Type Certificate
Any propeller that appears on the Original Equipment Manufacturer's (OEM) approved equipment list (found on the Aircraft Type Certificate Data Sheet) is automatically approved for that application. No further paperwork is required. Replacing a worn propeller with a new propeller of the same make and model is the easiest route to follow because it requires no approval. As long as the propeller you select is listed by the OEM, you can bolt on the new propeller and go. It's just that simple.

One-time Field Approval
More subjective in nature, the One-time Field Approval changes for every situation and is heavily dependent on the personality and experience of the FAA representative. In general, the more reasonable the request, the more likely it is to be granted. For example, field approvals are usually easier to get for aircraft serial numbers lower than what is officially approved for a particular aircraft. Obtaining field approval for serial numbers higher than what is approved by the OEM, or that involve a different engine, will be more difficult. There are only two things for certain about the One-time Field Approval:

  • It requires the endorsement of the FAA
  • It has to have some degree of technical justification

Experimental Certificate
The Experimental Certificate is an option available only to people who are classified as experimental aircraft owners or operators. Theoretically, you can install any propeller you desire if you are in this category. However, you should at least contact the propeller manufacturer for advice and a list of the possibilities best suited for your aircraft and engine.

Supplemental Type Certificate (STC)
The FAA issues an STC for propellers that have passed rigorous and the extensive testing but which are not listed on the OEM's approved equipment list for a particular aircraft. The STC is the easiest way to modify an existing airplane after it is out in the field. Most owners, operators, and mechanics who wish to upgrade propeller performance will take the STC route. Although commonly used, the STC is a complicated document that is not commonly understood. For that reason, our discussion on this page will focus on the STC and call your attention to the factors that affect warranty, performance, and safety.


Types of STCs
The Single-Component STC
Single-component STCs are the most common involving one particular propeller that has been approved for one particular aircraft. For example, the single-component STC is commonly used to upgrade an aircraft from a two-bladed to a three-bladed propeller. It may also be used by owners/operators who have never been satisfied with the performance of their original propeller.

The Combination STC
The combination STC is a package deal that involves multiple components, such as a propeller and engine upgrade. Although less common than single-component STCs, the combination STC is gaining popularity because of the integral relationship between propeller and engine. It just makes sense that a brand new propeller will not perform at expected levels if it is powered by a sick engine and vice versa.

Obtaining an STC
It costs tens of thousands of dollars and a significant investment of time to secure an STC. Besides dealing with FAA, the STC holder often works with the original manufacturer, tests and evaluates the propeller, and pays for flight performance testing and stress surveys. Developing the STC for a simple, one-propeller changeover for a particular aircraft can cost as much as $20,000. Consequently, STC holders typically charge a flat fee for a copy of their STC paperwork and often sell the complete package, i.e., propeller(s), mounting hardware, and paperwork.

The Implications of STC Ownership
The STC holder may be the original propeller manufacturer, the original aircraft manufacturer, or an independent entity. When someone other than McCauley obtains an STC on a McCauley product, we usually begin selling that STC propeller directly to the STC holder to facilitate delivery to the end user. You should be aware, however, that the following peculiarities of STC ownership may have an affect on your after-sale support:

  • STC holders do not always work with the original propeller manufacturer prior to obtaining STC approval from the FAA. STC holders who have not worked with McCauley may not have a full understanding of our products, their applications, and how they are likely to perform on their respective aircraft.
  • The FAA usually does not notify the original propeller manufacturer when it grants an STC to someone other than the OEM. As such, we have no way of knowing about each and every STC approved for our propellers by the FAA.
  • STC holders who do not work with McCauley while obtaining an STC for our products often neglect to inform us once that STC is granted.

For all these reasons, you should contact the manufacturer of the STC propeller you are installing. Find out if the OEM is aware of the STC and any potential problems that may exist. Contact the STC holder directly to discuss the performance changes you should expect. Also, request a list of owners and call them.

Warranty and the STC Conversion
The warranty that comes with the STC conversion has two different aspects:

  • The warranty on the propeller
  • The warranty on the performance.

The STC holder is responsible for problems with installation adjustment and performance. Nonetheless, we are often contacted by owners and operators having adjustment or performance trouble that are not propeller-related. Among others, these may include problems with the engine, the engine mounts, cowling configuration, or the airframe.

It may help to understand that the aircraft used to secure the STC was probably in prime condition. Most aircraft in the field are not. Consequently, the STC holder's certification data is often "best case." Owners of aircraft in average condition may not see the same changes in performance. Again, contact the STC holder directly, request a list of owners, and call them.

Troubleshooting
The best way to determine whether or not your problem is propeller related is by process of elimination. As such, you should avoid introducing too many variables at once. For example, you should not convert from a two-bladed propeller to a three-bladed propeller immediately after an engine overhaul. Recently overhauled engines frequently cause vibration, a reaction that can be mistakenly blamed on a new propeller installed at the same time.

In this example, your best course of action would be to try out your recently overhauled engine using the two-bladed propeller. If you experience vibration, and you had not before, then you will know immediately that it is an engine problem, not a propeller problem. Make sure everything is working properly under usual operating conditions before installing any STC conversion.


Vital Service Information: Two Steps to Better Service
1) Pay attention to our service bulletins
The service bulletin is the strongest document a manufacturer can write. Contrary to popular belief, we cannot write an Airworthiness Directive, nor can we ask the FAA to write one on our behalf. ONLY THE FAA CAN WRITE AIRWORTHINESS DIRECTIVES. We cannot overemphasize this point. When any of our STC conversions in the field requires a modification, we issue a service bulletin to alert owners and operators. Our service bulletins contain information related to flight safety and aircraft performance. Please give them the attention they deserve.

2) Choose a reputable propeller shop
FAA certification is no guarantee that a propeller shop is top notch. Whether you are repairing/overhauling your propeller, upgrading your aircraft, or simply replacing one propeller for another just like it, give us a call. We would be happy to provide you with a list of McCauley Authorized Propeller Service Centers.

 

Propellers by McCauley
McCauley Propeller Systems- a TEXTRON company