Helicopter Avionics That Are Cool

If you have ever travelled to the Dallas-Fort Worth, TX, metropolitan area, you know that it is pretty darn big. Everything in Texas is big, right? About 45 miles west of Fort Worth is the small town of Mineral Wells at the intersection of highways 180 and 281. It is the home of Cool City Avionics, and it has come up with some great new avionics for the helicopter market. Here is a little bit about them, in their own words.


To develop a line of affordable, high-technology, automatic flight control products that will forever change the general aviation helicopter industry by making automatic flight control and stability augmentation systems affordable.


Cool City Electronics Inc. was formed in 2001 to produce commercial electronic products for the transportation industry. Initial products included control systems and wiring harnesses for highly-sophisticated three-wheeled vehicles. In 2003, the company started work on the architecture for a new line of instrument flight rules (IFR)-capable helicopter automatic flight guidance control system products.

In the fall of 2004, Cool City Avionics was formed to design, manufacture and market a line of innovative, affordable digital flight control systems for general aviation helicopters and airplanes.


Cool City Electronics personnel have more than 400 years of combined experience in the automatic flight control industry — specifically in designing, manufacturing and installing automatic flight control systems for general aviation fixed-wing aircraft, coupled with more than 40 years of experience in the helicopter industry.

One of the principals, and other staff members, were founders of one of the industry-leading autopilot companies. In addition, their helicopter experience goes back to before “the helicopter war” in Vietnam, and includes service with one of the helicopter industry’s largest OEM manufacturing companies.

The Cool City Electronics staff has a high level of understanding of the FAA certification process that comes from conducting a multitude of TSO qualifications, and more than 3,000 STC approvals for automatic flight guidance and control systems (AFGCS). Some of our personnel have served as FAA engineering branch managers, FAA designated engineering representatives (DERs), designated manufacturing inspection representatives (DMIRs), designated alteration station (DAS) department managers and staff coordinators. The company created an FAA-approved quality control and management system to ensure the manufacture of high-quality products.

Each department at Cool City Electronics is represented by individuals who have served in leadership positions in previous aviation companies, with many having held leadership positions specifically in the autopilot industry.

From this combined experience comes a new line of products that take full advantage of today’s technology in circuit components, sensors and drive systems, to fulfill all of the flight control requirements of small- and medium-sized helicopters, while also providing new functions and significantly lowering system costs for some large helicopters.

Industry Impact

Owners, operators and pilots of small and medium-sized helicopters can enjoy the many benefits offered by stability augmentation systems and automatic flight guidance control systems that for decades have been available on larger helicopters and fixed-wing aircraft.

Cool City Avionics’ stability augmentation systems and autopilot products are lightweight, high performance, professional-grade systems that improve the safety, stability and functionality of small and medium-sized helicopters, while giving the pilot more time to manage the cockpit workload efficiently.

Let’s focus on Cool City Avionics’ new stability augmentation system (SAS), stability control augmentation system (SCAS) and autopilot. I had the pleasure to interview Jim Irwin, Cool City Avionics’ president and CEO.

Helicopter Maintenance – What are the system names and what are the system functions?

Irwin – The RW (rotary wing) systems are in two categories, i.e., autopilot-only systems identified as HAP-100 and HAP-150. HAP stands for helicopter autopilot with 100 being a two-axis system and 150 being a three-axis system. Autopilots with SCAS are identified as HFC-100 and HFC-150 systems. HFC indicates helicopter flight control, including SCAS, while the 100/150 designation still indicates the autopilot axes of control. All SAS/SCAS systems are generally two-axis, although three-axis SCAS can be provided in special cases.


Helicopter Maintenance – What size helicopter are the systems designed for?

Irwin – The systems were designed for helicopters that include both piston-powered and turbine-powered aircraft. One of our in-process STCs is for the Sikorsky S-61 model at 20K pounds gross vehicle weight, so we will cover small, medium and large helicopters. We have an ambitious STC plan for implementation after the initial approval on the Robinson R44, which will include the R66, American Eurocopter models, Bell models, MD models and others, including Enstrom.

The system can operate aircraft with mechanical control systems without hydraulic boost. It will take a while to accomplish the certifications planned. The order of STCs often depends, in the end, upon available aircraft and the demand for specific models from the field. As a result, it is helpful for those interested to call us and ask about plans for their model helicopter.  

Helicopter Maintenance – For what Part FAR are the systems designed?

Irwin – At the technical standing order (TSO) level, the systems have been qualified for FAR Part 27 and 29. STC projects are in process for both normal and transport categories, including instrument flight rules (IFR). 

Helicopter Maintenance – Are the systems designed to be single or dual?

Irwin – The basic system will be available in the four variants. The HFC-150 system has been designed for single pilot IFR at the TSO level. It provides independent SAS/autopilot functions, integral gyro sensors and air data for redundant sub-systems. An altitude (ALT) mode, vertical speed (VS) mode and indicated airspeed (IAS) mode, along with other IFR features, are also provided. The system will also be available in dual versions using Moog Valve servo control actuation, with a later variant available using an integrated, partially-redundant electromechanical servo for medium-size helicopters. The dual system allows pilot selection of the active system or automatic transparent selection accompanied by annunciation in the event of a failure. Both systems are full-up, complete systems, with full navigation coupling and with the capability for redundant air-data and gyro sources, and each with their own integral back-up systems.

Helicopter Maintenance – In describing the autopilot (AP) systems, you are also talking about modes that I normally associate with a flight director (FD). Are these modes part of the autopilots?

Irwin – Yes, our autopilot systems combine the features of both an autopilot and what you refer to as a flight director in one digital flight guidance computer (DFGC). The DFGC does have a steering drive output to command FD steering bars, either single or two-cue types.

Helicopter Maintenance – With respect to the flight director, what lateral and vertical modes does it have? How many can be active at a time?

Irwin – With the AP and FD functions fully integrated, functionally the difference is whether the AP servos are engaged. The FD is selected when the AP is “on” (engaged) simply using the controller-mounted AP on-off switch to switch the AP “on”. Deselecting AP (off) with the controller switch will disconnect the autopilot and leave the existing modes for FD operation active and displayed. A second selection of the AP switch will remove (stow) the FD display and clear the modes. Disconnecting the AP with the remote disconnect switch will cancel and clear the modes and all functions, except SCAS.

Helicopter Maintenance – Can flight director modes be flown manually in SAS?

Irwin – Yes, the SAS function is completely independent of the AP and will continue to operate with the AP disengaged. The SCAS function is not independent of the autopilot, because it uses AP servo control position feedback to tailor the SCAS response to reduce pilot control inputs in turbulence. If the AP position feedback fails, the SCAS will automatically revert to SAS functionality, and operate without the control feedback.

SAS series actuator operations are transparent to the pilot, moving only the aft control elements to the swash plate. They are very quick response, low-authority elements, while the AP operates with slower, parallel, full-authority servos. Both systems complement each other, but either system will operate without the other for redundant stabilization in the event of failure.

Helicopter Maintenance – What sensors does the system require?

Irwin – The basic system includes integral, solid-state gyros and air-data transducers for all basic flight functions, but it will need a HDG bug and directional gyro input for the heading mode. It will also require navigation inputs for radio coupling — VOR/ILS/GPS modes. The system was designed as an “attitude” control system, with the integral gyros used as an IFR back-up safety system. As a result, system performance is improved when external attitude information is available. Autopilot use in hover flight requires attitude gyro references and heading references. However, all other modes and functions perform their intended functions regardless of the gyro sensor sources.

Helicopter Maintenance – Must the sensor inputs be digital?

Irwin – No, the system will accommodate analog DC synchro signals as well as ARINC 429 data.


Helicopter Maintenance – Do you use “smart” servos (signal processing in the servo)? How about linear actuators?

Irwin – The servos do not have internal processors. However, they each provide integrity monitors that act independent of the DFGC during normal operation and failure modes, to determine proper servo command tracking and operation. The servos and actuators include motor controllers, direct position feedback sensors and integrity monitors that can stop errant servo/actuator operation, while also reporting servo operation back to the DFGC for system for evaluation and annunciation.

Helicopter Maintenance – With so many uses of the word digital being used in so many different systems today, what does that word imply with regard to your system?

Irwin – The system uses four digital signal processors and all control laws are executed in the processors. The DFGC is rack mounted, along with the air-data elements and the system configuration module. They are mounted on the same rack and automatically connect to the installed DFGC when it is in the rack. All these components communicate digitally by design. The servos and actuators use stepper motors controlled by analog control signals and monitors. The controller is an analog switching device read by the computer at about 20 Hz.

Helicopter Maintenance – What digital buses are used?

Irwin – The system has seven ARINC 429 input ports and one output port, plus a controller area network (CAN) bus output port for service diagnostics or external data recording. The system also has an independent 48-channel integral data logger function.

Helicopter Maintenance – How many LRUs are in the system? 

Irwin – It depends upon the number of axes controlled. The HAP-100 AP has four LRUs total. The HAP-150 adds yaw damping internally and a servo, total five LRUs. The HFC-100 and 150 add internal electronics and two SAS/SCAS actuators for a total of six and seven LRUs, respectively.


Helicopter Maintenance – Does the system employ built-in-test (BIT?)

Irwin – Yes, the system employs a comprehensive power-up self test (POST) at every power–up event. The self-test requires several seconds and tests communications between units and functional checks, as well as all critical system monitors, both analog and digital. A portion of the test is conducted during system initialization and completed during the first aircraft taxi/hover movement, which allows additional dynamic sensor checks to be conducted. The POST test must be passed 100 percent before AP operation is allowed. In addition to the POST test, there are continuous BIT tests conducted during operation, which also include the monitors. During operation, failures detected and annunciated allow continued system operation for any function that is not affected by the failure, until the first system power-down.

Helicopter Maintenance – Are there system options? How about sensor options?

Irwin – First, the systems can be converted from basic systems to a higher level by adding the SAS and yaw damper functions which convert the systems to the new higher level model designation. All systems are standard with full radio coupling for navigation, including GPS-V (or +V) when wide area augmentation system (WAAS) GPS is available. Field conversions to upgrade to three-axis or SCAS could be considered options, but result in a changed model designation. Second, we have an optional “orbit” mode for use by those that conduct circular orbits, like law enforcement, electronic news gathering, etc. The option adds switch hardware and operating software. This option requires a three-axis AP system and a heading card synchro heading input (HSI) or air data attitude heading reference system (ADHRS) heading input, and a GPS navigator capable of outputting position references, such as a GNS-430 or equivalent. The system accepts analog or digital sensor signals from heading/HSI systems, attitude gyros and digital signals from air data systems.


Helicopter Maintenance – Any special equipment required for field maintenance/troubleshooting procedures?

Irwin – Dealers will be required to have a servo/actuator test box to assure proper actuator centering during aircraft rigging checks after the initial installation. A laptop computer will be required for operation of the diagnostics program disc for service diagnostics. The dealer will need a National Instruments USB 8472 CAN bus adapter for the diagnostic port interface. Service diagnostics can be conducted over the internet, direct to the factory from the aircraft being serviced, in real time.

Helicopter Maintenance – Who would typically do an installation?

Irwin – All installations will be conducted by Cool City Avionics’ authorized dealers.

Helicopter Maintenance – Who will own the STC?

Irwin – All STCs are conducted and owned by Cool City Avionics. Installation data will be furnished with each installation kit.

Helicopter Maintenance – On average, how long should an installation take?

Irwin – That depends upon the system model, the installation design and the equipment interface requirements. Initial estimates should be about two to 2.5 man-weeks. After installation familiarity, HAP systems may require as little as one man-week or less, with HFC systems requiring 1.5 man-weeks to two man-weeks.

Helicopter Maintenance – Will system/LRU programming be done in a particular manner, like via laptop computer or other device?

Irwin – Not applicable to this system generally. However, configuration module changes could be conducted in the field using a laptop, but will be controlled and programmed at our facility due to FAA approval process requirements. No programming or modification should be necessary. The systems are customized during manufacture for the interface requirements of the equipment specified in the order process, by the purchasing dealer, for the aircraft installation involved.

Helicopter Maintenance – To what category is the system certified?

Irwin – Autopilots are major aircraft modifications and require STC certifications, which will cover the appropriate category of the aircraft model. The systems are TSO-approved to the latest FAA TSO for automatic flight guidance control systems (AFGCS), TSO C198, and the minimum operational performance standards (MOPS) RTCA DO-325. According to the FAA, these systems will be the first full systems approved under these specifications, which now cover airplane and helicopter systems.

Helicopter Maintenance – How will you address the issue of the same system but different aircraft types?

Irwin – Each certified installation will be covered by an STC certification. Variants of the same basic aircraft model can often be added to an STC based upon known or examined similarity, but each model approved for the installation will have been evaluated and identified to the installer.

Helicopter Maintenance – Can you share some lessons learned?

Irwin – For SAS/SCAS installations, we will provide information we have learned about the safest and most efficient way to remove and replace the control tubes for actuator installation, using the factory service Information as a guide. Additionally, actuator installation in the tubes, which will typically be done by Cool City Avionics, is part of the install kit, so the control tubes are an R&R exercise normally.

The install kit includes the system wiring harness pre-wired into the rack with the RFI/EMI shield in place. It is only necessary to terminate the outer cable ends and “wring” the completed harness for errors. The cable and wire terminations are identified. All of the cables are special, very supple, double-shielded and cut to length, with safety excess for routing variations.

There you have the new and cool autopilot/SAS and SCAS systems from Cool City Avionics.