April 23, 2013 

Mr. Jonathan Moritz 

Delta Engineering 

13 DRBA Way 

New Castle, DE 19720 

jemoritz@delta-engineering.com 

(302) 325-9351 

Introduction: 

Delta Engineering, 13 DRBA Way, New Castle, Delaware 19720, submits this petition, under the 

provisions provided for in Title 14 Code of Federal Regulations, Part 11, as a petition to grant exemption 

to Title 14 CFR § 25.251 to change “Vd” to “Vmo/Mmo with validated CFD to Vd”. Delta Engineering is 

requesting this exemption for our FAA STC projects that modify the external configuration of the aircraft 

to install large radome’s. Currently the STC projects us the Equivalent Level of Safety process to allow 

for flight testing to Vmo/Mmo with validated Computer Fluid Dynamics to Vd. 

Delta Engineering has completed several FAA STC’s with large radome’s with successful results (no 

affect to 25.251) for example ST02884NY-D, ST02927NY-D, ST02905NY-D, ST02890NY-D,

ST03163NY-D for aircraft models 737, 747, 777, A330, A340, A319, A320. 

Below table outlines the current 25.251 requirements. 

Amendment 25.251 

0 (b) Each part of the airplane must be shown in flight to be free from excessive vibration, under any 

appropriate speed and power conditions up to at least the minimum value of allowed in Sec. 25.335. 

The maximum speeds shown must be used in establishing the operating limitations of the airplane in 

accordance with Sec. 25.1505. In addition, it must be shown by analysis or tests, that the airplane is free 

from such vibration that would prevent safe flight under the conditions in Sec. 25.629(d). 

23 (b) Each part of the airplane must be shown in flight to be free from excessive vibration, under any 

appropriate speed and power conditions up to at least the minimum value of allowed in Sec. 25.335. 

The maximum speeds shown must be used in establishing the operating limitations of the airplane in 

accordance with Sec. 25.1505. In addition, it must be shown by analysis or tests, that the airplane is free 

from such vibration that would prevent safe flight under the conditions in Sec. 25.629(d). 

72 (b) Each part of the airplane must be shown in flight to be free from excessive vibration, under any 

appropriate speed and power conditions up to at least the minimum value of VD allowed in Sec. 25.335. 

The maximum speeds shown must be used in establishing the operating limitations of the airplane in 

accordance with Sec. 25.1505. In addition, it must be shown by analysis or tests, that the airplane is free 

from such vibration that would prevent safe flight under the conditions in Sec. 25.629(d). 

77 (b) Each part of the airplane must be demonstrated in flight to be free from excessive vibration under 

any appropriate speed and power conditions up to VDF / MDF. The maximum speeds shown must be used 

in establishing the operating limitations of the airplane in accordance with Sec. 25.1505. 
Current Method used for 25.251: 

Delta Engineering proposes using a validated CFD and performing a flight test to Vmo/Mmo. 

In order to address 14 CFR 25.251 vibration and buffeting requirements, the following will be 

completed : 

1. Perform CFD analysis of the aircraft both with and without the radome, at the following speeds : Mmo, 

MDive and 1.5G recovery at MDive.

2. Demonstrate analytically that the aerodynamic flow field does not change significantly between Mmo

and MDive.

3. Include in the flight test plan, flight to Vmo and MMo in order to demonstrate no adverse vibration and 

buffeting, and no adverse change to handling characteristics due to the radome installation.

4. Extrapolate that the radome installation is aerodynamically insignificant and therefore compliant to 14 

CFR 25.251(b).

Public Interest & Safety:

This exemption is in the interest of the public as to allow flight testing for such FAA STC’s to only 

Vmo/Mmo instead of Vd with valid CFD to Vd. 

This exemption is also in the public interest to avoid FAA resources on creating Equivalent Level of 

Safety’s for each FAA STC project. 

There would be no adverse effect on safety if this petition for exemption was granted as the methods 

proposed in this exemption are already FAA accepted/approved. 

Jonathan Moritz 

Delta Engineering