Par 7 Page 12 him or her from other piloting responsibilities. Some examples of documented instabilities in experimental airplanes during some flight regimes include:
(a) Following a small airspeed deviation slower than the trimmed speed, the airplane will continue to decelerate until it stalls, unless the pilot intervenes. This is an example of negative longitudinal static stability.
(b) Following a small airspeed deviation faster than the trimmed speed, the airplane will continue to accelerate until it exceeds VNE, unless the pilot intervenes. This is an example of negative longitudinal static stability.
(c) Following a small rudder pedal displacement, the airplane will continue to yaw to a larger sideslip angle, unless the pilot intervenes with opposite pedal displacement. This is an example of negative directional stability.
(d) Following a deviation (either faster or slower) in airspeed, the airplane alternates slowing and speeding up with each oscillation larger than the previous one, until it either stalls or exceeds VNE. This is an example of negative longitudinal dynamic (phugoid) stability.
(e) After establishing the airplane in a bank angle, it continues to roll toward increasing bank, unless the pilot applies opposite aileron. This is an example of negative spiral stability.
(5) These examples pertain to several experimental airplane designs, hundreds of which have been flying for years. Although this statement may appear to minimize the concern, it is intended to illustrate that some experimental airplanes have behaviors that can be kept in check under normal circumstances, but can rapidly develop into an emergency situation unless the pilot remains absolutely vigilant at all times. A common analogy is balancing a broomstick in the palm of your hand: it is possible, but doing it successfully while copying a clearance or programming a Global Positioning System (GPS) is much more difficult, and if it tilts too far, no amount of effort or concentration can save it.
(6) The airplane’s control system plays a major role in the pilot’s impression of its stability, controllability, and maneuverability. An airplane with weak stability but high control force requirements might feel more stable because the pilot would have to apply a substantial force to the controls to cause a small control surface deflection. If that small deflection, however, resulted in an unexpectedly large airplane response, the pilot might have to spend an inordinate effort to keep the responses manageable. Likewise, an airplane with very low control forces and highly maneuverable response can easily lead to over-controlling with a series of alternating inputs in an attempt to arrest airplane excursions. Both scenarios of airplane-pilot coupling are pilot-induced oscillations and can escalate very rapidly into an out-of-control situation.
(7) The freedoms allowed in experimental airplane design and also in individual builders’ construction decisions may significantly influence the airplane’s stability and controllability. The following list provides some examples of what may affect stability and controllability; all have an effect that can range from negligible to disastrous:
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• Small errors in wing or tail incidence angles;
• Irregularities in lifting surface finish;
• Improper CG location or calculation;
• Addition of flight control gadgetry like springs, bobweights, and dampers;
• Aileron-rudder interconnects; and
• Addition of protuberances like antennas or scoops.
(8) If your airplane exhibits negative stability behavior, consult a reliable source, such as the designer or type club, to determine whether this is inherent in the design or peculiar to your airplane. Modifications may be available to minimize the undesirable characteristics; be extremely careful about making changes to your airplane. If you do make changes, develop a thorough and well-conceived flight test plan for evaluating not just the characteristic to be improved, but also unintended changes to the existing characteristics.
c. Recommended Flight Training. Know your airplane’s systems, characteristics, limits, and recommended normal, abnormal, and emergency procedures before you begin flying.
Consult the kit vendor for advice. Discuss your situation with type club members and owners/builders of your airplane model. Internet forums and chat rooms may provide valuable information, but remember that the participants may or may not have the technical expertise you seek, and their airplanes may exhibit different stability characteristics than yours. A thorough airplane check-out by a qualified instructor, preferably with recent experience in your airplane make and model, is always a good idea. If you built the airplane yourself, consider obtaining this training from the kit vendor, preferably in your airplane, although the company demonstrator may provide sufficiently similar characteristics. If you purchased your airplane from a previous owner, learn all you can from him or her.
NOTE: Pilots transitioning to experimental airplanes must be aware that the habits and reflexes they learned flying TC’d airplanes may yield hazardous results when used in experimental airplanes.
d. Additional References (current editions).
• AC 23-8, Flight Test Guide for Certification of Part 23 Airplanes.
• AC 61-98, Currency Requirements and Guidance for the Flight Review and Instrument Proficiency Check.
• The Advanced Pilot’s Flight Manual, Kershner, Iowa State University Press.
• Flight Testing Homebuilt Aircraft, Askue, Iowa State University Press.
• The Illustrated Guide to Aerodynamics, Smith, TAB Books (Division of McGraw-Hill).
• Aerodynamics for Naval Aviators, Hurt.
8. TRANSITIONING TO AN UNFAMILIAR AIRPLANE. Even if a pilot is experienced in and knowledgeable about the characteristics of a particular airplane, transitioning to a new airplane of the same family can still be challenging. This is especially true in experimental airplanes, as system design, switch and control appearance and location, and types and locations of indicators may be different, even in airplanes of the same model.
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a. Transition Training. In order to complete a successful transition to a new airplane, in addition to the training and experience described in the group appendices, pilots should follow an organized methodology to become familiar and competent in the new airplane. This study or training should include, as applicable:
(1) Systems:
• Fuel,
• Electrical,
• Hydraulic,
• Flight control,
• Landing gear,
• Ventilation/heating/pressurization,
• Avionics,
• Powerplants,
• Autoflight systems,
• Flight instruments,
• Warning systems,
• Oxygen systems, and
• Emergency equipment.
(2) Procedures:
• Normal,
• Abnormal, and
• Emergency.
(3) Performance:
• Takeoff and landing,
• Climb,
• Cruise,
• Descent,
• One-Engine Inoperative (OEI), and
• Glide.
(4) Limitations:
• Weight,
• CG,
• V speeds,
• Kinds of operation,
• Crosswind, and
• Landing surface.
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b. Systems. When “checking out” in any airplane, regardless of the airplane’s size and complexity, or the pilot’s experience level, approach airplane systems with an open mind. Even in simple airplanes of a similar design or even the same model, the innovation of individual designers and builders may cause problems for a pilot new to the airplane.
(1) One way of studying airplane systems is to think about the flow of that system. All systems have some kind of flow. For example, a fuel system is understandable if studied from the perspective of how fuel moves from the filler port through to the cylinder or combustion chamber and exhaust. Consider the following questions when learning the fuel system of a carbureted single-engine airplane by using the flow method:
(a) Fuel enters a filling port.
• What kind of fuel is required?
• What color is it?
• Where is the port?
• How many ports are there?
• Is there an order to refueling?
• Is there a special grounding procedure or fuel additive required?
(b) Fuel is stored in a tank.
• How many tanks are there?
• Is there a requirement to use one particular tank when taking off and landing?
If so, why?
• Are there any fuel tank drains? Where are they? How do you check them?
• How is fuel quantity measured? In what units?
(c) Fuel is controlled by a fuel valve.
• Where is the valve?
• Where is the cockpit control?
• Can you find and operate it by feel?
• What positions are there?
• How is position selection indicated?
• If “both” is a position, how do you know fuel is being supplied from both tanks?
• What is the procedure to change tanks?
• Is there a maximum fuel imbalance level?
• How do you balance fuel in flight?
• Which tank or kind of tank is used for takeoff and landing?
• Does the fuel tank selection affect the quantity indicator(s)?
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(d) Fuel leaves the tank at a fuel line pickup.
• Is there an electric fuel pump in the line?
• When is it supposed to be on?
• Where is the switch?
• What indication of fuel pressure is there?
• How do you know if the fuel pump is working?
(e) Fuel enters the engine at the carburetor or injectors.
• How does the pilot control the mixture?
• When is “Full Rich” required?
• When is the fuel mixture leaned?
• What indications are there for leaning?
• What is the desired leaning procedure for best power? For best economy?
• When does the pilot use carburetor heat, if applicable?
• How is its operation checked?
(2) Similarly, a description of electrical systems can work by considering the flow of current from the battery or generator(s)/alternator(s), to the buses on the airplane, to the appliances and components that use electrical power. Study flight controls by looking at the pilot input in the cockpit, through the mechanical linkages and hydraulic boost assists, to the actual movement of the control surface.
(3) Any system on the airplane is capable of description by the flow methodology. This offers a lot of opportunity to understand the components and their location and function, which can give great insight to normal, abnormal, and emergency procedures. Also, understanding the location and function of accessible components can greatly enhance safety in that preflight inspections can be more effective in identifying unsafe or marginal conditions.
c. Procedures.
(1) The use of checklists was not common to early aviators. In fact, the modern checklist was not widely adopted until a takeoff accident involving the Boeing 299, the prototype which became the B-17 bomber, in which a highly experienced and skilled crew attempted to take off with the controls locked. The thought at the time was that the Boeing 299 was so complex an airplane that the procedural steps required to fly it needed to be written down and checked off.
(2) Today, checklists are expected in every kind of airplane, even the simplest. There are hundreds of accident and incident reports over the years involving pilots who declined to use a checklist because they thought their airplane was “so simple to operate, why do I need one?”
Many a gear-up landing, loss of control on takeoff due to miss-trim, and engine failure due to fuel mismanagement, as well as crashes on takeoff with locked controls, were avoidable by use of a checklist. Checklist usage should be emphasized during all phases of aircraft operation.
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(3) In order to safely operate an airplane, develop procedures that take into account the airplane’s design, limitations, performance, and intended use. Procedures generally fall into the following categories:
• Normal,
• Abnormal, and
• Emergency.
(a) Normal procedures. All aircraft should have normal, abnormal, and emergency procedures checklists. If there are no checklists for your airplane, make one and base it on the designer’s recommendations (or manufacturer’s recommendations for TC’d aircraft) and your study of the airplane systems. If it is simple, consider making it a placard with critical checklist items. When designing a checklist, consider as a logical cockpit pattern, or flow, the prestart, start, and shutdown procedures. Normal procedures include:
• The preflight inspection,
• Start,
• Taxi,
• Pre-takeoff,
• Takeoff,
• Climb,
• Cruise,
• Descent,
• Approach and landing,
• After landing, and
• Shutdown operations that are part of every flight.
(b) Abnormal procedures. These address circumstances when systems or components of the airplane are not operating properly or have failed, but the situation is not threatening.
Generally, abnormal procedures are those that do not rise to full emergency status on their own, even in more challenging conditions. An example might be the in-flight failure of an electric trim system. The abnormal procedure may include securing the system (trim switch off, or trim circuit breaker pulled). After applying the procedure, there should only be a slight increase in pilot workload.
(c) Emergency procedures. These procedures require a timely response to ensure continued safe flight and may involve significant changes in flight profile. Obvious emergencies are:
• Engine failures,
• Fires,
• Loss of pressurization at altitude,
• Loss of a control system, and
• Loss of flight instruments, avionics, or navigation systems determined by the pilot to be critical to flight.
Par 8 Page 18 NOTE: The level of risk, in continued operation may be related to the conditions the airplane is flying in; an alternator or generator failure is likely a mere inconvenience in day VFR local operations, but could be an emergency during a night or IFR flight.
(4) Perhaps the most important factor in the successful outcome of a system failure is the proper identification of a problem; the flow methodology helps here, as well. By understanding the flow, a pilot can easily identify the normal function of a system. For example, in an engine, the engine oil pump circulates the oil under pressure. When the engine is cold, the oil is more viscous (thicker). After engine start, the oil pressure will be fairly high and will likely remain so until the oil heats up, becomes less viscous (thinner), and circulates more freely. Therefore, it is normal to see high oil pressure immediately after start, and to see more moderate pressure in flight. There may be something seriously wrong if the pilot observes high oil pressure in cruise, as well as low oil pressure after start. A pilot cannot tell when a system is malfunctioning unless he or she knows what it looks like when operating normally.
(5) Once the pilot has identified the situation and determined the correct checklist to apply, knowledge of the controls and indicators related to that system will prove invaluable because it may be that system performance is compromised by malfunctioning valves, pumps, relays, and other components relied upon by the checklist. Understanding what the checklist item is, and what the expected outcome is of the individual steps taken, can help the pilot identify failed components and develop a course of action that best answers the problem.
d. Performance and Limitations.
(1) While there may not be any official performance or regulatory limitations specified for an experimental airplane, pilots must be able to identify an acceptable, safe flight envelope and operate within it. Base this envelope on the designer’s or manufacturer’s data and the experience gained in the flight test program and post-test phase operation for experimental aircraft. Title 14 of the Code of Federal Regulations (14 CFR) part 91, § 91.103 requires the pilot to become familiar with all available information concerning that flight. For aircraft with no approved flight manuals, the information must include other reliable information appropriate to the aircraft. For example, the pilot should be able to ascertain aircraft performance under expected values of airport elevation and runway slope, aircraft gross weight, wind, and temperature.
(2) For example, if demonstrated that the stall speed of the airplane is more than the designer’s data indicates, adjust accordingly any takeoff and approach, and landing data derived from the standard airplane. Actual flight experience, coupled with close observation of density altitude, can validate that adjusted data and give the pilot a high level of knowledge about his or her specific airplane’s performance. Until the pilot achieves that level of knowledge, avoid operations to smaller fields, particularly at higher weights and density altitudes.
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9. REQUEST FOR INFORMATION.
a. Contact Information. You may direct questions about this AC to:
Federal Aviation Administration Flight Standards Service, General Aviation and Commercial Division, AFS-800 800 Independence Avenue SW, Washington, DC 20591 Telephone: 202-267-1100 Fax: 202-267-1078
b. Web Site. You may also find more information on the Flight Standards Web site at http://www.faa.gov. On this Web site, you will find links to Flight Standards programs, aviation safety inspector (ASI) handbooks and documents, the current aviation regulations of 14 CFR, ACs, and other FAA information.
ORIGINAL SIGNED by /s/ John Barbagallo Deputy Director, Flight Standards Service
Appendix 1 APPENDIX 1. AIRPLANE FAMILIES FAMILIES AND EXAMPLES. This appendix describes the families of airplanes considered in this advisory circular (AC). However, an airplane can be included in one or more families. For example, the Long EZ is Nontraditional Configuration or Controls, and High Inertia and/or Low-Drag. In a case such as this, the pilot should develop an integrated risk mitigation training strategy drawn from the appendix for each family. These families are broad, and include example airplanes which display characteristics of the family at different levels. Pilots should consider this in developing their risk mitigations. For example, in the Low-Inertia and/or High-Drag family, both the Piper Cub and the Kolb Firefly are included. Both exhibit low-inertia and highdrag characteristics, but the Kolb Firefly significantly more so. See Appendix 2 for more information on the categorization of example airplanes into families.
TABLE 1. AIRPLANE FAMILIES AND EXAMPLES Family of Airplanes Examples of Experimental Airplanes Examples of Comparable Type Certificated (TC’d)/Special Light-Sport Category Aircraft (SLSA) Airplanes Refer to Appendix Notes:
Light Control Forces and/or Rapid Airplane Response Zodiac 601, RV series, Pitts, Lancair 200 & 300 Series Pitts (TC), Extra 300, Grumman AA-1, Swift, Zlin 3
Low-Inertia and/or High-Drag Challenger II, Flight Star, Kolb Firefly, Rans S-12, Pietenpol, Fly Baby Quicksilver GT-500, Cub, Champ 4
High Inertia and/or Low-Drag Skyfly, SX300, Questair Venture, Glasair, Lancair, Long EZ Columbia, SR-22, Mooney, Piper Comanche 5
Nontraditional Configuration or Controls Varieze, Velocity, Dyke Delta, Wright Flyer, Quickie, Air Cam, Breezy, Long EZ Sky Arrow, Lake Amphibians 6 If training in the experimental airplane is not possible and is going to be done in a comparable TC’d or SLSA, take care to ensure that there is commonality in the nontraditional configuration or controls.
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Family of Airplanes Examples of Experimental Airplanes Examples of Comparable Type Certificated (TC’d)/Special Light-Sport Category Aircraft (SLSA) Airplanes Refer to Appendix Notes:
Nontraditional or Unfamiliar Airplanes System Operations Auto conversions, other than the Volkswagen or Corvair, (e.g., two-cycle, Wankel engines) and folding/removable wing airplanes Civil Aviation Regulation (CAR) 3 Airplane (systems), Remos, Soloy Conversion Airplanes 7 If training in the experimental airplane is not possible and is going to be done in a comparable TC’d or SLSA, take care to ensure that there is commonality in the nontraditional configuration or unfamiliar system operations.
Nontraditional or Unfamiliar or System Component Maintenance Requirements Auto conversions, other than the Volkswagen or Corvair, (e.g., two-cycle, Wankel engines) and folding/removable wing airplanes Dependent on airplane-specific characteristics.
8 Ground training should be specific to maintenance and preflight procedures of these airplanes.
Specialty Airplane One-off airplane, limited production, unique, extremely high power-to-weight ratio, jet-powered, electric-powered, turboprop-powered, rocket-powered Dependent on airplane-specific characteristics.
Airplanes may be available with some similar characteristics or systems.
Consider retaining the services of a qualified test pilot.
9 Conduct in-depth ground training on the operation of the specific airplane.
Recommend pilot follow guidance in the current edition of AC 90-89, Amateur-Built Aircraft and Ultralight Flight Testing Handbook, for first 40 hours of flight testing if flight training is not available in the specific airplane.
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APPENDIX 2. CATEGORIZING DESIGNS OR MODELS
1. AIRPLANE CATEGORIES. The purpose of this appendix is to orient the reader to the aircraft families which are most likely associated with the identified airplane designs or models.
This appendix describes a general categorization of common experimental amateur-built airplanes into the families considered in Appendices 3 through 6 of this advisory circular (AC).
Significant effort has been made to properly categorize each model; however, any evaluation of this kind is somewhat subjective. Construction variances, installed equipment, and other factors may cause a model to have characteristics of a family not identified in this table. As mentioned in Appendix 1, different airplane models categorized in a family may display varying degrees of the characteristic of that family. The reader is advised to seek additional information from the designer, kit vendor, or type clubs. Another source of information is the Comparative Aircraft Flight Efficiency (CAFE) Foundation, which maintains a Web site at www.cafefoundation.org.
2. RISK MITIGATION. The risk mitigations described in subparagraph 6a(3) apply to all models of airplanes whether listed or not. In addition, if there is an “X” in one or more family columns, see the appropriate appendix or appendices for guidance to develop your specific risk mitigation training. If a model is not listed in this table, you must decide what family or families apply based on airplane characteristics. In the event that a model in this table has no “X” marks indicating categorization to the families considered in Appendices 3 through 9, the subparagraph 6a(3) guidance applies.
NOTE: For the most up-to-date information regarding this appendix, please refer to the General Aviation Operations Branch (AFS-830) Web page at the following address:
http://www.faa.gov/about/office_org/headquarters_offices/avs/offices/afs/afs8 00/afs830/. This information will be located in the Resources section. As updated information becomes available this Web site will be updated to reflect the affected changes. The date of the information on the Web site should be compared to the publication date of this AC to determine which is more current.