3022 Sterling Circle – Suite 200, Boulder, Colorado 80301 Phone: 303-449-1105

www.specinc.com

November 23, 2015

Docket Management Facility

US Department of Transportation

1200 New Jersey Avenue

SE West Building Ground Floor Room W12‐140

Washington, CD  30590

RE:  Limited exemption from 14 CFR 91.881 – Learjet 25 N999MF  

Dear Federal Aviation Administration and US Department of Transportation:

The purpose of this Petition for Exemption is to request a limited exemption from 14 CFR

91.881, Stage 3 Noise Restrictions, for a Restricted Category atmospheric research Learjet 25,

N999MF.  This aircraft operates exclusively in support of U.S. government sponsored research

projects.   

Background:

N999MF is a Learjet 25 operated by SPEC Inc. to conduct atmospheric research during

government research projects.  The maneuverability, high altitude capability, and ruggedness of

this aircraft have made N999MF an irreplaceable asset in numerous high profile government

projects researching the physics of climate change.  Attachment A provides details of N999MF

instrumentation and research capabilities.  Projects within the last three years in which this

aircraft participated include:

 U.S. Department of Energy, Pacific Northwest National Laboratory ‐ Project Sparticus.  

Aircraft conducted high altitude in situ cloud particle sampling and analysis during the

Atmospheric Radiation Measurement (ARM) Climate Research Facility's Small Particles

in Cirrus (Sparticus) Field Campaign.

 National Science Foundation ‐ Project IceT.  Aircraft conducted joint investigations with

the National Center for Atmospheric Research C‐130 during the Microphysics of

Maritime Tropical Cumulus Clouds research project.
 National Aeronautics and Space Administration ‐ Project SEAC4RS.  Aircraft conducted

in situ cloud particle and aerosol data gathering in support of microphysical

instrumentation and scientific analysis during the SEAC4RS Field Campaigns.  Aircraft

flew joint missions with the NASA ER‐2, DC‐8 and WB‐57.

 United States Navy ‐ Project 3V‐CPI.  Aircraft conducted in‐flight cloud physics studies

for comprehensive data‐reduction and analysis for Cloud and Precipitation Particle

Imager Data.

 National Aeronautics and Space Administration ‐ Project MACPEX. Aircraft conducted

in situ cloud research that resulted in more accurate understanding of ice particles in

Cirrus clouds.  N999MF served as a pathfinder for the NASA WB‐57, helping that aircraft

avoid convective turbulence.

SPEC Inc. is currently working with the Denver FSDO and a FAA Designated Engineering

Representative to obtain approvals to instrument a Stage 3 compliant Learjet 35.  Since this

process has been delayed by engineering and regulatory issues, SPEC is seeking an exemption to

continue to research operations for the next 2 years, or until FAA approvals are obtained for a

replacement Learjet 35.

SPEC considered and rejected equipping N999MF with hush kits for operational reasons.  Since

the research instrumentation causes the aircraft to operate in a high drag configuration, often at

maximum certified weights, it was determined that the additional weight and drag of the hush

kits would further degrade the aircraft’s performance to an unacceptable degree.  Additionally,

no hush kit manufacturer has flight test data showing the effects of the kits at the high altitudes

and slow speed regime in which research is often conducted.   

Public Interest:

Granting of this Exemption Request is in the public interest since this aircraft provides a unique

platform for atmospheric research flights that gather the data used for climate modeling.   

Atmospheric research and accurate climate modeling are clearly viewed as an urgent priority by

the U.S. government.  The current administration has tasked NASA and other federal research

agencies with the goal of better understanding atmospheric physics and effects on climate.  

N999MF, as a Restricted Category research aircraft, has meaningfully contributed to these

scientific studies.  Attachment B is a letter of support from NASA explaining the importance of

N999MF to these studies.

To ground this aircraft at this critical time in government studies will adversely affect public

interest by degrading the quality and tempo of scientific research of atmospheric physics.  

Mitigation of Adverse Effects:

SPEC Inc. scientists and flight crews are committed to minimizing the adverse effects of noise

inherent in operating a Stage 2 aircraft.  To minimize impacts, the following limitations are

followed:
 Flights are solely conducted for the purpose of scientific research during government

research projects.  Limited flights may be conducted before and after projects for

weather instrument research and development, research instrument calibration and

data validation.

 Flights are not to originate or end at noise sensitive airports.  To the extent possible,

joint‐use bases such as the Johnson Space Center Ellington Field are used.  The aircraft’s

home base (KBJC) experiences frequent military operations, and there has never been a

noise complaint as a result of N999MF operations.

 During flight operations, N999MF uses an FAA approved call sign: ICFLT xx.  Use of the

call sign enables FAA controllers to immediately understand the needs and limitations of

Restricted Category research operations (such as the need to avoid noise‐sensitive

areas).   Preflight coordination is done with controlling FAA ATC facility.

 Crew annual Recurrency Training is conducted in a FAA approved simulator and does

not utilize the actual aircraft.

 The vast majority of flights are conducted during daylight hours.  Only very rarely do

research flights need to be conducted after dark.  No repositioning flights are conducted

after dark.

Sincerely,

R. Paul Lawson, PhD

Senior Scientist