So, What's in it for the aircraft owner?
By Jim Sparks
Technology in the area of aircraft electronics continues to expand at a rapid rate. The new equipment available is not only intended for the airlines and military applications. On the contrary, significant advancements have been made and tailored to the general aviation market.
So what are the incentives for the single engine aircraft owner to install a new avionics package? Well in some cases certain modifications may be driven by regulation. For example, the use of older VHF aircraft radios not meeting a frequency tolerance of .003 percent was decided to be illegal for transmissions by the Federal Communication Commission on Jan. 1, 1997. Transmitting on these radios is illegal; receiving radio frequencies is not a problem. In other cases support for older equipment is dwindling and repair capability may no longer exist.
An upgrade package on any aircraft should include a great deal of preplanning. The more thought that goes in on the front end will have exponential effects on system longevity and reliability.
A primary consideration in the decision process should always be the aircraft primary mission. An aircraft used for transporting sky divers perhaps within a 10-mile radius of its home airport would probably not require sophisticated and multiple navigation systems. Whereas a long-range business aircraft operating in high density air routes will require more complex equipment with adequate backup as to allow continued operation should a failure be recognized while in flight. With all the new equipment on the market sometimes the "I want" exceeds the "I really need" situation which can sometimes result in staggering increases in cost of the installations.
Prior to making any decisions regarding equipment, a prudent approach is to sit down with a reputable avionics technician who can explain the interfacing capabilities of different devices. Numerous cases are on record where an operator has tried to mix and match different equipment brands only to find they do not speak the same language. This can usually be resolved by incorporating converters, however, the additional engineering and components can change what looked like a reasonable upfront cost into a money pit. Support for morphadite systems is also often difficult to obtain except from perhaps the installer.
Some of the primary considerations prior to investing in an avionics upgrade should include:
Upgrade ability. When changes come out (as we all know they will) how difficult and expensive will they be to incorporate?
Mission change. Should the aircraft need to make trips to Europe issues like communication radio frequency spacing at 8.33 kHz vs. 25 kHz will need to be considered.
Use of existing equipment. In some cases certain pieces of hardware may be compatible with newer technology devices. This option should be explored as significant cost savings may be realized.
Technical support and logistics. Can the system problems be addressed by a wide range of repair shops and are spare parts readily available?
Weight change. Although new technology devices are in general much lighter than similar devices of yesteryear, the tendency to install additional systems may have an impact on the aircraft payload.
Power requirements. Like with weight change most new electronics consume significantly less electrical power than their predecessors. Anytime aircraft electrical loads change, a load analysis should be conducted.
Of course anytime an aging aircraft goes in for an avionics upgrade issues such as condition of existing wiring should be taken into account. It is often more prudent to consider that the installation of new wiring may reduce the number of failures plus, in many cases with today's electronics, the dependency is on data buses. Wire technology has also improved over the years where the ability to conduct electron flow has increased while overall the weight of the wire is reduced.
New systems often require the installation of new antennas. Undocumented installations can result in ongoing problems not to mention reduced radio performance or possibly structural failure. The same criteria also apply to new equipment installation. Mounting of radio racks will require a structural evaluation.
Several means of approval can be used to satisfy airworthiness requirements. In some cases the aircraft manufacturer will introduce service data that will provide all the information needed to accomplish the installation. It is important though to make sure the data does contain an FAA approval prior to the installation. Generally the next most favorable means of supporting an avionics upgrade is with a Supplemental Type Certificate (STC). An existing STC can often be a less painful route than obtaining new.
Steps to obtaining a new STC
1) Verify that the subject (aircraft) of the initial STC carries a valid US Type Certificate Data Sheet.
2) Open a project with the FAA;
3) Conduct an aircraft survey;
4) Compile a complete electrical and structural engineering package to install the system;
5) Carry out fatigue or damage tolerance analyses for antenna installations or any other fuselage penetrations;
6) Submit the engineering package to the FAA for approval, including: a master drawing list, FAA approved electrical and structural drawings, electrical load amendment, electromagnetic interference (EMI) test procedures, ground test procedures, flight test procedures, flight manual supplement, and a weight and balance amendment.
The project is then placed on hold until a type inspection authorization (TIA) is issued to the applicant by the FAA;
- Have the installation kit manufactured in accordance with the engineering;
- Have the installation kit inspected for conformity to the engineering by an FAA Designated Manufacturing Inspection Representative (DMIR) or Designated Airworthiness Representative (DAR).
- Install the system;
- Have the installation inspected for conformity on the aircraft and approved by an on-site FAA DAR.
To be witnessed by a FAA representative:
1) Conduct ground tests;
2) Conduct Electro Magnetic Induction and Radio Frequency Induction EMI/RFI tests;
3) Conduct flight tests;
4) Submit test results to the FAA and request issuance of the STC.
Steps to adapting an existing STC
- Obtain licensing agreement to use the appropriate STC. According to U.S. federal law, the licensing agreement must be issued to any entity (kit manufacturer, installing agency, etc.) using the data. An approved installation kit provider can apply to the FAA for Parts Manufacturer Approval (PMA) for this specific kit and eliminate the conformity inspection requirement, once they have the licensing agreement;
- Create an engineering data package to accommodate changes between the STC subject aircraft and your fleet;
- Submit engineering data package to an FAA DAR for approval;
- Have the installation kit manufactured in accordance with the engineering;
- Install the system;
- Conduct ground tests;
- Return the aircraft to service.
The company selected to provide engineering and system integration kits for a project should be able to perform all the engineering, testing, kit manufacturing, and FAA coordination requirements listed in either of these two situations as part of their service.
The installation of a new autopilot is more complex and involved than the average avionics installation. It's certainly more than just mounting black boxes connected to power and ground. When installing a new auto flight system you are tying into the primary flight controls of the aircraft, interfacing with navigation equipment, and connecting to the aircraft electrical system.
For the new autopilot to work properly and up to its maximum performance, it is dependent on all the systems it is linked to and their proper operation. If any of these systems are not performing up to their peak, the auto pilot performance could be compromised. Therefore, at the beginning of an installation it is recommended that the installer check the performance of interacting systems.
Check to see if the control cable tensions meet the manufacturer's specifications. Check to assure the control travel is within specified limits and that there is no stiffness or binding in the aircraft flight control system. When connecting to the electric system, check for the proper voltage output and be sure the input voltage is clean and free of induced signals.
Navigational and other avionics equipment must be delivering optimum outputs to assure that the autopilot, which is interfacing with them, will perform properly. Be sure and check the outputs against manufacturer's specifications at the outset.
When routing the harness avoid bundling with transmitter coaxes and any cable carrying high current or alternating current. It is also important when dealing with wire installations to observe all recommendations for minimum wire diameter for a specific current flow and wire length. Another issue is bend tolerance and clamping. Coax cables and bus wire are impedance critical and too hard a bend or an overtightened clamp or wire tie can have a dramatic effect as far as signal loss.
In many facilities the receipt and unpacking of an avionics kit is done in the receiving department or the parts department. It is not unusual for the system to be handled by numerous persons prior to getting to the installer. Each of these "stops along the way" can be a place for hardware or paperwork to get misplaced. While extraordinary efforts to assure that correct drawings and piece parts are all included with the system by the supplier, errors have been known to occur. If you don't catch the shortage until the aircraft is in the hangar and disassembled, an unpleasant installation delay can occur while a new part or drawing is procured.
Performing an inventory of the contents of the autopilot kit prior to the start of the installation can save time and help you to keep your delivery commitments to the customer.
Most pilots are not qualified avionics technicians. However, it is critical to the efficient repair of these systems that an established line of communication between the technicians and flight crew exist. The last thing a tech wants to read on a squawk sheet is the phrase "INOP." It tells almost nothing other than there is a problem. Frequently gremlins appear intermittently and it can be very frustrating to repeatedly bring the aircraft back to the shop for repair. Even in these times of maximized frustration, avoid the word "INOP." The more information a flight crew can supply the technicians, no matter how trivial it seems at the time of fault detection, can often be the key that unlocks the mystery of the fault.
Avionics upgrades can often be the way to bring an older aircraft up to meet current production machines. If handled properly with adequate planning a long trouble-free life can be anticipated at a price that is within the range of most aircraft operators. Of course new avionics systems may also provide interface with various airframe systems, which can pose new challenges to aircraft maintenance technicians. Air data computers as an example now take the place of airspeed switches in systems from the good old days. With the state-of-the-art systems now in use it becomes increasingly difficult to determine where airframe stops and avionics start.