September 11, 2013

U.S. Department of Transportation

Docket Operations

West Building, Room W12-140

1200 New Jersey Avenue, S.E.

Washington, D.C. 20590

Subject: Petition for Exemption,

Delta Engineering for Project ODA-2337-01

Title 14 CFR § 25.571(e)(1), amendment 25-96

Subject: Request for immediate exemption from Title 14 CFR §25.571 (e)(1) bird strike substantiation to 

Vc.

Introduction:

In accordance with Title 14 CFR Part 11, Delta Engineering is petitioning for an immediate exemption from Title 

14 CFR § 25.571 (e)(1) showing that the aircraft is capable of completing a flight after impact with a 4 pound bird 

with relative speed of Vc. Delta Engineering’s STC project, ODA-2337-01 is for the installation of a Panasonic 

GCS antenna system, under a large composite radome, on a Boeing 737-900ER aircraft. Delta Engineering 

wants to use Vmo in place of Vc for compliance with Title 14 CFR § 25.571 (e)(1). 

Title 14 CFR § 25.571 (e)(1) amendment 25-96 states, “Impact with a 4-pound bird when the velocity of the 

airplane relative to the bird along the airplane’s flight path is equal to Vc at sea level or 0.85 Vc at 8,000 feet, 

whichever is more critical;” As provided in Title 14 CFR § 25.1505 Vc can equal Vmo; also Vmo is established 

as the maximum speed that is not to be deliberately exceeded. Vmo is published and FAA approved in the 

Airplane Flight Manual and the Type Certificate Data Sheet, A16WE. Whereas Vc is not a published number,

available to the public and when provided we may not been able to trace to the TCDS. 

Supporting data for the requested exemption:

In NPRM 55 FR 29756 the FAA provided a position the Vmo was not appropriate since Vmo is an operational 

speed whereas Vc is a design speed. Although keeping the design criteria consistent is a good objective it does 

not necessarily change the level of safety. As provided above Vc is allowed to be equal to Vmo. Since the 

event of striking a bird is related to the operation of the aircraft using the maximum operational speed of the 

aircraft vs design speed of the aircraft does not reduce the level of safety. Title 14 CFR 25.571(e) requires 

corrective action by the flight crew, if necessary, after the bird strike which could include further operational 

speed limitations. 
Title 14 CFR §25.1505 requires the establishment of maximum operating airspeed (Vmo) which is not allowed to 

be greater than Vc, but Vc can equal Vmo. Title 14 CFR §25.1505 also establishes that only inadvertent 

operations of the aircraft are allowed to exceed Vmo. 

Title 14 CFR §25.571 prior to amendment 72 required “Impact with a 4-pound bird at likely operational speeds at 

altitudes up to 8,000 feet”. The aircraft type certificated prior to amendment 72 have not been shown to be 

unsafe or more suspect to bird strike. For aircraft that were certified using 25.571 prior to amendment 72 

compliance, a speed of 250 knots has been used as the likely operational speed. Although, an operational speed 

of 250 knots is possible, 250 knots is the likely speed below 10,000 feet.

The FAA has granted multiple time limited exemptions from Title 14 CFR 25.571(e)(1) for the same type 

alterations. FAA Exemption 10847, 10848, 10849, 10851, etc. These exemptions remove compliance with 

Title 14 CFR § 25.571 (e)(1) for a period of one year. The FAA would not grant exemption from 25.571(e)(1) if 

the aircraft was unsafe, even for one year. 

Proposed Requirements for Equivalent level of safety:

Since the aircraft is not allowed to normally operate above Vmo ensuring compliance with Title 14 CFR 

§25.571(e)(1) using Vmo will not impact the level of safety. The non-traceable manufacturers data presented to 

Delta Engineering indicates Vc=Vmo. Delta Engineering wants to the following wording for Title 14 CFR 

§25.571(e)(1) “Impact with a 4-pound bird when the velocity of the airplane relative to the bird along the 

airplane’s flight path is equal to Vmo at sea level or 0.85 Vmo at 8,000 feet, whichever is more critical” 

Public Interest:

Granting this exemption would benefit the public because some of the manufactures consider the Vc data as 

proprietary data and will not disclose the information. Without the manufacturers Vc data, this will impact the 

ability of modifying aircraft that require compliance with 25.571(e)(1) and the applicant using later amendment 

levels. Granting this request for exemption would not adversely affect safety because of the extremely low 

probability of a bird strike when the aircraft. And the aircraft is not to be operated at speeds above Vmo. The 

aircraft operator is aware of Vmo limitation because of the visual and audible warnings.

Conclusion:

Although using Vc for compliance with Title 14 CFR 25.571(e)(1) is more consistent, using Vmo does not reduce 

the level of safety. Delta Engineering wants to the following wording for Title 14 CFR §25.571(e)(1) “Impact 

with a 4-pound bird when the velocity of the airplane relative to the bird along the airplane’s flight path is equal to 

Vmo at sea level or 0.85 Vmo at 8,000 feet, whichever is more critical”

Sincerely,
John A. Moritz

Delta Engineering

13 DRBA Way

New Castle County Airport

New Castle, Delaware 19720

Phone (302) 325-9337

E Mail jamoritz@delta-engineering.com