5. Aircraft Operations

5.1 Scope

This section describes the aircraft platforms and instrumentation, the aircraft base at Ponca City, the flight

mission modules, crew rest, mission decisions and planning, in-flight decisions, debriefing, post-mission quality control, and post-experiment data processing and quality control.

5.2 Aircraft Platforms and Instrumentation

5.2.1 King Air General Characteristics

This aircraft is a Beechcraft King Air model 200T, operated by the University of Wyoming. Its payload is 14,000 LB; its endurance 4.25-4.5 hours, corresponding to a range of about 1600 km at 100 m/s The King Air operates at a true airspeed of 80-110 m/s. Typical data-sampling speed is 160 kt (30 m/s)


Table 5.1 UW King Air Scientific Payload for CASES 97






Air temperature

Reverse flow

-50 to 50 C

0.5 C

0.006 C

Air temperature


-50 to 50 C

0.5 C

0.006 C


Cambridge Sys Model 137C3

-50 to 50 C

1.0 C > 0 C

2.0 C < 0 C

0.006 C

Mag. heading

King KPI 553/Sperry/C14-43

0-360 deg

1 deg

0.02 deg

Static pressure

Rosemount 1601

0 - 1080 mb

0.5 mb

0.003 mb

Static pressure

Rosemount 1201FA1B1A

0 - 1034 mb

0.5 mb

0.06 mb

Geometric Alt.

Stewart Warner APN159 Radar Alt.

60,000 ft


0.24 ft

Geometric Alt.

King KRA 405

2,000 ft

3% < 500 ft; 5% > 500 ft

0.48 ft


Rosemount 1332

0-85 mb

0.2 mb

0.005 mb


MRI Turbulence Meter

0-10 cm2/3/sec

0.5 cm2/3/sec

0.1 cm2/3/sec

Azimuth from sta

King KNR615 VOR

360 deg

1 deg

0.02 deg

Distance from sta

King KNR705A DME

200 naut. mi.

0.4 naut. mi.

0.1 naut. mi.


Tremble 2000 GPS

±90° lat; ±180° long

100 m

0.000172 deg


Honeywell Laseref SM

±90° lat; ±180° long

100 m

0.000172 deg

Ground velocity

Honeywell Laseref SM

0 - 1095 kt

1 m/s after correction

0.0039 kts

Vertical velocity

Honeywell Laseref SM

±32,788 ft/in

1 m/s after correction

0.03125 ft/in

Pitch/roll angle

Honeywell Laseref SM

±90 deg pitch; ±180 deg roll

0.05 deg

0.000172 deg

True heading

Honeywell Laseref SM

180 deg

0.2 deg

0.000172 deg

Differential pressure

Rosemount 858AJ/1332

±15 deg

0.2 deg

0.00375 deg

Liquid water cont.

In-house CSIRO hot wire

3 g/m3

0.2 g/m3

0.0003 g/m3

Engine torque


2230 ft lb


0.2 ft lb

Event markers

In-house (10/station)




Video record

forward-looking camera, downward-looking camera, and voice recording


H2O and CO2 vapor

LICOR 6262 Gas Analyzer

0-75 mb (H2O) 0-3000 ppm (CO2)

1% ± 1 ppm @ 350 ppm

0.1 mb 1 ppm

Pyranometer (up and down)

Eppley PSP (0.285-2.8m m)

0-1400 W/m2

5 W/m2

0.08 W/m2

Pyrgeometer (up and down)

Eppley PIR (3.5-50m m)

0-700 W/m2

15 W/m2

0.04 W/m2

Radiation therm. (up)

PRT-5 (9.5-11.5 m m)

-20 to + 75C

0.5 C

0.1 C

Radiation therm (down)

Heimann Kt-19.85 (9.5-11.5 m m)

-50 to +400 C

0.5 C

0.10 deg for 10s


5.2.2. NOAA Twin Otter General Characteristics

The NOAA Twin Otter is a DeHavilland DH-6 Twin Otter, Series 300. It is unpressurized, and can operate at altitudes up to 25,000 ft. It can hold up to 4,800 pounds. With a fuel load of 2,500 pounds, its capacity for personnel and cargo is 2,300 pounds. At sea level and an airspeed of 120 kt (65 m/s) , it can stay airborne for 4.2 hours. Typical data-gathering speed is 110 kt (60 m/s). Instrumentation Payload. Figure 5.2 - Twin Otter Aircraft Instrumentation)

5.3 Aircraft Base

The Ponca, City, OK airport will be the aircraft base of operations. This facility meets the needs for hangar space, power, fuel, runway length, ability to make coordinated takeoffs, and ILS landing system. Coordination with the CASES-97 main operations center is discussed in Section 2.

5.4 Flight Mission Modules (Appendix 5A, Modules 1-6)

5.4.1 Use of Flight Mission Modules

Flight mission modules, described in the Appendix, are designed as part of aircraft missions to enable estimates of boundary layer budgets of momentum, sensible heat, and water vapor. They can be used for single or coordinated aircraft missions. Aircraft will fly more than one mission a day; these can be single-aircraft (to optimize time coverage) or dual-aircraft (to optimize spatial coverage) missions.

5.4.2. Low-level Flux Runs

The FAA has granted low-level flight restriction waiver to the NOAA Facilities for CASES-97. The NSF Facility will operate without a waiver under FAA Rule 91 which specifies low-level flight restrictions.

Low-level flux runs require track lines that meet FAA requirements (avoid houses, cattle pens, major highways). Preliminary tracklines have been determined; these will be refined by the pilots, and marked by GPS-determined end points before low-level data runs are made. The flight lines will be used to define the lowest-level (100-200 feet) leg of any of the flight patterns.

These flight lines are based upon Rule 91 which also governs the NOAA waiver, and they have been passed on to Wichita FAA officials. Flight operations are more flexible in the central and eastern parts of the watershed than the western part of the watershed which is close to an urban area (Wichita, KS) and a Military Operations Area (MOA).

5.4.3 Ferry from Ponca City to CASES-97 Domain

Aircraft missions out of Ponca City will begin with a ferry to the Oxford profiler (37.2743N; 97.095W) west of Winfield, KS at either 500 ft above the highest point along the route or 200 ft below cloud base. Upon reaching the profiler, the aircraft will continue on its track for one minute, and then perform a sounding from 100 ft to above the capping inversion. It will then commence the flight pattern chosen for that particular mission.

When there are more than two missions for an individual aircraft in one day, the aircraft will land and refuel at Augusta airport in the middle of the watershed.

5.4.4 Data Assurance Strategies

Low-level flux runs require minimal deviations from straight and level flight. Roll and pitch angles need to be less than five degrees unless perturbed by atmospheric turbulence. Turns to avoid obstructions along the track should be anticipated and made with minimal bank (flat turns). However, safety must not be compromised.

Intercomparison legs will be part of each coordinated mission. The scientific flight directors will log the altitude and start and stop times for each intercomparison. Aircraft Self-Calibration Maneuvers (Appendix 5A, Modules 7-10)

When there are clouds, each mission should include a pop-up sounding that just barely penetrates the cloud base to check temperature-dewpoint depression (Appendix).

Scientific flight directors will also be responsible for insuring each mission contain maneuvers for checking wind velocity biases (Appendix). Aircraft-Aircraft Intercomparisons

Spatially coordinated missions will require that the two aircraft fly wing-to-wing formation along the Ponca-Winfield ferry for intercomparison purposes. Temporally coordinated missions will require a rendezvous and a wing-to-wing intercomparison of five minutes (or whatever is logically possible) before the outgoing aircraft departs for base.

For planning purposes, 20 minutes of flight time should be reserved for intercomparisons. Comparisons with other instrumentation

Comparisons with profilers and surface flux stations will be part of each mission. Surface flux intercomparisons will be at as low above the surface as possible; comparisons to profilers should be at height(s) corresponding to routine profiler observations. Aerial Photos

At least once during the experiment, it would be useful to obtain aerial photographs of each surface stations. A locally-owned, single-engine aircraft can be used for this purpose.

5.5 Communication

Radio contact will be necessary between aircraft as well as between the aircraft and the CASES Coordination Center in Augusta. The primary use of radio contact will be safety (coordination with balloon launches), boundary layer mean wind (for orientation of cross-wind legs) and boundary layer height (communication of sudden changes). Secondary needs include comparisons of boundary layer height, surface-mixed layer comparisons of flux, surface temperature, and meteorological parameters (especially wind).

122.925 MHz is the dedicated frequency for CASES-97. A VHF base station will be located at the CASES Coordination Center at the ABLE Office in Augusta, KS.

5.6 Flight Operations Procedure

Flight mission choices will reflect the accomplishment of the operational objectives associated with the scientific objectives. Crew rest and aircraft availability must also be taken into account in the mission choice decision. Grossman, LeMone, and McMillen will discuss flight mission candidates the night before. There will always be two choices of missions (a Plan A and Plan B), even if Plan B is "Cancel."

5.6.1. Flight-planning time line Decision Sequence (See Table 2.1)

If an IOP for the following day has been ordered, detailed flight planning will begin at 1630 among the PIs at Ponca City and the pilots. Once plans are firm, they will be faxed to the CASES Control Center by 0800 CDT the day of the IOP. Flight Operations Sequence in Ponca City

With emphasis on following the diurnal cycle, early-morning takeoffs (~ 0830 LDT) will be frequent for one or both aircraft. In such cases, the items under Takeoff - 3 hours should be taken care of the night before.

Takeoff - 3 hours

Takeoff - 1.5 hours

5.6.2 In-Flight Operations Decisions

While the Scientific Flight Director may suggest certain flight operations and changes to these operations while in flight, the Flight Commander makes the final decision. This safety principle will never be compromised.

5.6.3. Debriefing in Ponca City (for timing, see Section 2.2.1)

Each flight mission will include a debriefing after the mission is complete to include:

 5.6.4 Post-Flight Quick Look Data Processing

(a) reasonableness of the data in light of the scientific objectives,

(b) adequacy of averaging lengths for flux estimates,

(c) reasonableness of spectra and cospectra of the important variables

(d) intercomparison between aircraft and surface systems

(e) preliminary budget computations.

Probably only (a) (and possibly (d)) will be possible by the next operations meeting.

 The PIs need to be able to read the aircraft data in the field to evaluate the success of the aircraft and missions in fulfilling the scientific objectives. A common in-field data format would be highly advantageous. Facilities need to coordinate with the PIs to insure the post-flight data media and format are compatible with their hardware and software.

5.7. Post-Experiment Processing and Quality Control

5.7.1 Output format

A common output data format for both NOAA and NSF is strongly encouraged as this will greatly speed post-flight analysis. NETCDF format is suggested.

We expect three data sets to emerge:

 5.7.2. Data availability for quick look

5.7.3. Facility scientific interests

The Facilities are encouraged to take a scientific interest in the data they collect for CASES-97. If such a scientific interest arises within the Facility, coordination with CASES-97 PIs is encouraged as well.

Move to Operations Plan home page

Move to CASES home page

Move to MMM homepage

Email web page inquiries to: Ron Murdock, CASES webmaster at
Subject: CASES WWW page
Last Modified: 20 Aug 1997