AOPA Get Your Glass Sweepstakes Update -- The DER approval process

March 25, 2013

Sweeps Update

Project Update: June 19, 2008

The DER approval process

By Ian J. Twombly

One of the great joys with the sweepstakes project is scheming and brainstorming the fantastic upgrades we perform on each airplane. While some of these upgrades are well known to the industry and can be installed with minimal paperwork hassle for the shop, some are original alterations. These original alterations are time-consuming because of the extensive approval process. In most cases, that approval comes courtesy of a designated engineering representative, or DER.

“When a mechanic works on an aircraft he or she is generally either performing a repair, alteration, or preventive maintenance,” says Peter Stelzenmuller, owner of Penn Avionics, the shop that refurbished the sweepstakes airplane’s panel. Under the category of alterations, Stelzenmuller said, are both major and minor. A minor alteration only requires a logbook entry from a mechanic and can be things such as “installing a panel-mounted clock, installing an external GPS antenna on a non-pressurized aircraft, or replacing an existing nav-com with a new unit,” he says. Major alterations are covered in FAR Part 43 Appendix A, although Stelzenmuller said he thinks the list is vague. Instead, he said, a good guideline is whether the alteration requires a supplemental type certificate (STC), or POH supplement. In the end though, sometimes it comes down the local FSDO’s interpretation.

If the alteration is major, there are a number of different sources that can be sought for approval, including airworthiness directives, type certificate data sheets, and supplemental type certificates. But one of the most popular options is to use a DER, an independent engineer the FAA has certified to sign off on alterations. DERs are often called in to help with field approvals, a one-time FAA approval process for major alterations. Although most field approvals are used when a product has an STC for another make that is trying to be applied to the aircraft in question, Stelzenmuller says, they can be used for original alterations as well. But when is a DER required to obtain a field approval? According to Stelzenmuller, it’s obvious when a structural modification is necessary, but when in doubt, the FSDO can make a recommendation. “It is always a good idea to call the FSDO and discuss the proposed field approval before submitting the paperwork,” he says.

The panel approval

The Piper Archer sweepstakes airplane has a number of field approvals that were facilitated with DER approvals, the latest being the airplane’s one-piece metal panel. “Penn Avionics classified the panel replacement as major because the original panel was a structural part of the aircraft, and it significantly changed the design of the panel (to a one-piece panel design rather than the original two-piece upper/lower panel). Had this been a Cessna 172/182/210 with a removable (nonstructural) instrument panel and the new replacement panel was generally the same dimensions as the old removed panel, it may have been a minor alteration, Stelzenmuller says. The field approval process went as follows:

  • AutoCAD (computer-aided design) drawings of the proposed new panel layout were sent to the DER, as well as some detailed photographs. Penn created the preliminary CAD drawings representing inputs from AOPA staff and preliminary structural details. · The DER evaluated the overall alteration and performed calculations on load factors.
  • The DER then added various engineering details to the CAD package. These details included metal thickness, required stiffeners, hardware types, etc.
  • There was an on-going dialog between the DER and Penn as the engineering CAD package was put together.
  • Once the DER defined all the details, he generated a final set of CAD drawings and an FAA 8110-3 form, the FAA approved data for the panel alliteration.
  • Penn then performed the panel upgrade in accordance with the DER drawings and completed an FAA form 337 that references the DER’s 8110-3 form as approved data. One copy of the 337 form is sent to Oklahoma City, one kept on file at Penn, and one included with N208GG records.

Despite an intensive process, Penn was able to complete the approval within a matter of a few weeks, allowing us to pick up the Archer on schedule. Oxford Aviation also deserves credit because the shop completed a number of modifications involving a field approval. See if you can pick them out when you come visit your airplane at EAA AirVenture or AOPA Expo this fall.

Next week: Initial flight test numbers and observations

E-mail the author at ian.twombly@aopa.org