'i.,,' ' \ \( Advisory U.S. Department of Transportation CircularFederal Aviation Administration DATE: March 29, 1988 NOTICE
RECENT ACCIDENTS INVOLVING LARGE TRANSPORT
AND SMALL GENERAL AVIATION AIRCRAFT HAS
PROMPTED THE FEDERAL AVIATION ADMINISTRATION TO RE-DISTRIBUTE AC 20-117, HAZARDS FOLLOWI~G
GROUND DEICING AND GROUND OPERATIONS IN
CONDITIONS CONDUCIVE TO AIRCRAFT ICING DATED 12/17/82.
0 U.S. Department of Transportation Federal Aviation ----------···--······· ----------------- Advisory Circular Administration
CONSOLIDATED REPRINT This consolidated reprint incorporatea Chanae 1 Subject: HAZARDS FOI..I..CMING GROUND
DEICING AND GROUND OPERATIONS Date: 12/17 /82 Initiated by: AWS-100 AC No:
Change:
20-117 IN CDNDITIONS CX>NIXJCIVE 'IO
AIRCRAFI' ICING
1. PURPOSE. To emphasize the "Clean Aircraft Concept" foll<:Ming ground operations in conditions conducive to aircraft icing and to provide information to assist in compliance.
2. RELATED FEDERAL AVIATION REGULM'IONS (FAR) SECTIONS. Sections 121.629,
91.209, and 135.227.
3. BACKGROUND. Recent accidents involving large transport and small general aviation aircraft indicate that misconceptions exist regarding the effect of slight surface roughness caused by ice accumulations on aircraft performance and flight characteristics and the effectiveness of Freezing Point Depressant (FPD) ground deicing and anti-icing fluids. During developnent of information contained herein it was recognized that guidance information should be directed to all segments of aviation to include aircraft manufacturers; airline --- engineering, maintenance, service and operations organizations; aircraft maintenance and service personnel; and aircrews of all aircraft types and categories. Information contained herein therefore is general in nature for basic understanding p..irposes to facilitate developnent of standardized procedures and guidance by various segments of the aviation industry. The FAA will assist in developnent of specific industry standards and will p..iblish additional advisory information as necessary.
4. DISCUSSION.
a. Regulations were established by the Civil Aeronautics Board (CAB) in 1950 prohibiting takeoff of aircraft when frost, snow, or ice is adhering to wings, propellers, or control surfaces of the aircraft. These regulations remain in effect as cited under FAR 121.629, 135.227, and 91.209. '!he basis of these regulations, which are cx:moonly referred to as the clean aircraft concept, is kn<:Mn degradation of aircraft performance and changes of aircraft flight characteristics when ice formations of any type are present. 'lhese effects are wide ranging, unpredictable, and dependent upon individual aircraft design. '!he magnitude of these changes is dependent upon many variables and is thus unpredictable, but these changes can be significant. Wind tunnel and flight tests indicate that ice, frost, or snow formations on the leading edge and upper surface of a wing, having a thickness and surface roughness similar to iredium ·or coarse sandpaper, can reduce wing lift by as much as 30 percent and increase drag by 40 percent. These changes in lift and drag will significantly increase stall speed, reduce controllability and alter aircraft flight characteristics.
12/ 17/82AC 20-117 Thicker or rougher ice accumulations in the form of frost, snow, or ice deposits can have increasing effects on lift, drag, stall speed, stability, and control, but the primary influence is surface roughness relative to critical portions of an aerodynamic surface. It is therefore imperative that takeoff not be attempted unless it has been ascertained, as req~ired by regulation, that all critical components of the aircraft are free of adhering snow, frost, or other ice formations.
b. Most transport aircraft used in a:::mnercial transportation as \1/ell as sane other aircraft types are certificated for flight in icing conditions. It is emphasized that to date rotorcraft and nost small, general aviation fixed wing aircraft have not been certificated by the FAA for flight in icing conditions. Aircraft so certificated have been designed and denonstrated to have the capability of penetrating supercooled cloud icing conditions in the forward flight regime. This capability is provided either by ice protection equipnent installed on critical surfaces (usually the leading edge) or demonstration that ice formed, under supercooled cloud icing conditions, on certain unprotected components will oot significantly affect aircraft performance, stability and control. Ice, frost, or snow formed on these surfaces on the ground can have a totally different effect on aircraft flight characteristics than ice formed in flight. Exposure to \\'leather conditions on the ground that are conducive to ice formation can also cause accumulation of frost, snow, or ice on ice protected areas of the aircraft that are designed for inflight use only and that are oot designed for use during ground cperation. In addition, aircraft are considered airworthy and are certificated by the FAA only after extensive analyses and testing have been accorrplished. With the exception of analyses and testing to ascertain the flight dlaracteristics of an aircraft during flight in icing conditions, all analyses and certification testing are conducted with a clean aircraft flying in a clean envirorunent. If ice formations are present, other than those considered in the certification process, the airworthiness of the aircraft may be invalid and oo attempt should be made to fly the aircraft until it has been restored to the clean configuration. The ultimate responsibility for this determination rests with the pilot in carmand of the aircraft.
c. CCffll'Dn practice developed by the North .American and European aviation carmunity over many years of cperational experience is to deice an aircraft prior to takeoff. Various techniques of ground deicing were also developed.
The nost nodern of these techniques is use of FPO fluids to aid the ground deicing process and to provide a protective film of FPO (anti-icing) to delay formations of frost, snow, or other ice.
d. In scheduled airline cperations, where large ntnnbers of aircraft are dispatched, the process of assuring airworthiness nust be a team effort where each 11Ember of the team has specific duties an4 responsibilities. In the case of private aircraft operations, all functions may be performed by only one person, the pilot. Iri all cases, the pilot has the ultimate responsibility of ascertaining that the aircraft is in a condition for safe flight.
e. The only method currently kn<,,,m of !X)Sitively ascertaining that an aircraft is clean prior to takeoff is by close inspection. Under conditions of precipitation or where noisture can be splashed, blown, or sublimated ooto Par 4 2
12/17 /S2 AC 20-117 critical surfaces in subfreezing weather, many factors influence whether ice, frost, or snow may accumulate and result in surface roughness.
These variables are described in awendix 3 of this advisory circular (AC) but ·for convenience are listed as follows:
- Ambient Temperature
- Aircraft Surface Temperature
- Presence of Deicing Fluid
- Deicing Fluid Type
- Deicing Fluid l\gueous Solution (Strength)
- Precipitation Type and Rate
- Deicing Fluid Application Procedure
- Relative Humidity
- Solar Radiation
- Operation in Close Proximity to other Aircraft, Fquipnent, and Structures
- Operation on Snow, Slush, or Wet Surfaces
- Wind Velocity and Direction
- Aircraft Comp::>nent Inclination Angle, Contour, and Surface Roughness
f. Aircraft maintenance and q:,erations personnel neither have the capability to quantify the occurrence or the effects of the many variables that can influence whether ice, frost, or snow may form prior to takeoff, the surface roughness of ice formations, nor the effect that surface roughness may have upon aircraft performance and handling characteristics. Therefore, the time that may be considered a safe interval between ground deicing and takeoff cannot be estimated. Calculations of time incorp::>rating the effects of ooly a few of these variables (e.g., ambient telti)erature of 20°F, fluid strength of 50 percent, precipitation rate of 1/2 inch/hour, assl.D'Tled water content of snow of
0.1, and assumed surface film thickness of FPO fluid of 0.1 nm) reveals that -aircraft surfaces may remain free of ice formations (onset of FPO fluid crystallization) for approximately 10 minutes. Other variables listed above could reduce this time. Since neither the pilot in ~ nor ground support staffs have even these limited facts on hand, qu~titative judgements of time available between the ground deicing or anti-icing process and takeoff cannot be made.
g. The essence of flight safety following ground q:,erations in conditions conducive to icing is the clean aircraft concept. To understand the need for the clean aircraft concept requires thorough knowledge of: (1) The adverse effects that ice, frost, or snow can have oo aircraft' performance and handling Par 4 3
·--·..-·····--···---..;.;::==.-::::---::::::::===.;;:;=:::::::::""' ..._'.:_'.:_::"._::~--:::::-_-:.::.::::::...--::=.=.=.=.=.:=...==-=-=-=-=-=.:;;- qualities; (2) the various procedures that are available for aircraft grourrl deicing and anti-icing: (3) the capabilities and limitations of these procedures; (4) the variables that will influence the effectiveness of these procedures; (5) the critical areas of the parti~-ular aircraft: and (6) recognition that final assurance for a safe takeoff rests in pretakeoff inspection. Additional informa.tion to assist in developnent of this understanding and knowledge may be found in the appendices of this K'.. The success of the aviation corrrnunity to date is attributed to many years of experience oo the part of many oorrpanies where this knowledge has been gained, through experience, and passed oo in the form of policy_, procedures, quality assurance programs, and training programs.
5. /CCEPI'ABLE PRACTICF.S.
a. General. The clean aircraft ooncept is essential. The FAR makes the clean aircraft ooncept law. This law exists for flight safety reasons. The FAR states a general requirement but allows operators to corrply with the requirement in an appropriate manner, depending upon local circl.UllStances. The clean aircraft ooncept has been in effect since 1950. Many techniques of corrplying with the clean aircraft ooncept have been developed over the years by the aviation industry. Many of these techniques were developed prior to 1950 because of the need recognized by the aviation comnunity. The oonsensus of the aviation comnunity and the oonclusion readied by the FAA is that the ooly method of assuring flight safety following grourrl operations in oonditions oonducive to aircraft icing, is by either close inspection prior to takeoff to ascertain that critical aircraft components are clean {free of ice, frost, or snow forma.tions) or a determination that any formations are oot adhering to critical surfaces and will blow off in the early stages of takeoff roll. This oonsensus is valid regardless of the use of C\lrrently available FPO deicing fluids or the use of manual tedlniques of deicing. FPO fluids comronly used today should oot be considered to have anti-icing qualities for a finite period of time because a multitude of variables make it impractical to estimate that time. However, under certain oondition FPO fluids are known to be effective in retarding the formation of frost, snow, or ice and in this sense may be oonsidered to have anti-icing qualities {to prevent the formation of ice) for a period of time during ground storage (overnight or during brief layover) thus making the process of deicing (removing ice formations) simpler and in many cases l"W:?gating further deicing or treatment. It is erphasized, however, that the l"W:?ed for close inspection prior to takeoff remains. The following paragraphs are intended to provide suggested methods of assuring the clean aircraft ooncept.
( 1) Aircraft _Deici!19 and Anti-Ici!}g.
(i) An airplane may be cleaned of ice forma.tions {deiced) by any suitable manual method, by use of water, by use of FPO fluids, or mixtures of FPO fluids and water. To date manufacturers of rotorcraft have oot awroved use of FPO fluids for application to rotorcraft. Heated water, FPO fluids or aqueous solutions of FPO fluids are nore effectiv~ in the deicing process. The deicing and anti-icing process may be performed in ooe stage or nultiple stage processes as desired depending upon prevailing oonditions, concentration of FPO utilized, facilities available and deicing methods. In any case the freeze point of residual fluids (water, FPO fluids or mixtures) should oot be greater than 20°F below ambient or surface temperature whichever is less. Unheated FPO Par 4 4
12/17/82 AC 20-117 fluids or aqueous solutions are nore effective in the anti-icing process than heated fluids.
(ii) In conditions of freezing precipitation or high humidity when aircraft surface temperatures are near or below freezing and when it cannot be determined that snow or other ice crystal accumulations are oot ~hering and will blow off during initial stages of takeoff, surfaces should be anti-iced to retard the formation of ice prior to takeoff.
(iii) FPO freeze EX)int can be determined using refractive index techniques. FPO fluid manufacturers can suggest or supply suitable equipnent.
(iv) Critical surface terrperatures under many ciretm1Stances are found in the vicinity of integral wing fuel tanks. When fuel temperatures are higher than ambient, critical surface terrperatures will occur at other locations. These temperatures can be determined by direct maasurement or by estimating fuel terrperature. If surface terrperature is oot measured or estimated then the freeze EX)int of residual fluids should be the lowest EX)Ssible with available fluids.
(v) In conditions of oonprecipitation an anti-iced aircraft should be closely inspected to assure the freeze EX)int of residual fluids remain 20°F below ambient or surface terrperature whichever is lower. This is especially important when relative humidity is high.
(vi) Underwing frost should be renoved and, where practical, the surface anti-iced to delay re-formation of frost. See appendix 3 for ~itional information on this subject.
(2) Preflight Inspection. Preflight inspection should be performed inrrediately following or during the ground deicing and anti-icing process.
Areas to be inspected depend upon the aircraft design and should be identified in an inspection checklist. The inspection checklist should include all items reccmnended by the aircraft manufacturer and may be supplemented, as necessary, to include special operational considerations, but this checklist should include the following general items:
- Wing leading edges, upper surfaces, and lower surfaces
- Stabilizing device leading edges, upper surfaces, lower surfaces, and side panels
- High lift devices such as leading edge slats and leading or trailing edge flaps
- Wing lift spoilers
- All control surfaces and control balance bays
- Propellers
- Rotor Blades, rotor heads and controls Par 5 5
12/17/82 AC 20-117
- Critical rotor system devices such as droop stops
- Engine inlets, particle separators and screens
- Windshields and other transparencies necessary for vasibility
- Antennas
- Fuselage sections forward of stabilizing, control and lifting surfaces, propellers, rotors, or engine air inlets
- Exposed instrumentation devices such as angle-of-attack vanes, pitot-static pressure probes, and static ports
- Fuel tank and fuel cap vents
- Cooling and .APU air intakes/inlets/exhausts
- Undercarriage
(3) Once it has been determined through pre-flight inspection that the aircraft is clean and adequately protected, the aircraft should be released for takeoff as soon as possible. This is especially irrportant in oonditions of precipitation or high relative humidity.
(4) Pretakeoff Inspection.
(i) Fixed Wing_Aircraft (A) Just prior to taking the active runway for takeoff or just prior to initiating takeoff roll, a visual pretakeoff inspection should be ma.de.
The <XJ11)0nents to be inspected depend upon aircraft design. In sane aircraft, the entire wing, and p::>rtions of the enpennage are visible from the oockpit or the cabin. In other aircraft, these surfaces are so rexrote that only p::>rtions of the upper surface of the wings are in view. Undersurfaces of wings and undercarriage are oot viewable in any but high-wing type aircraft. A practice in use by sane operators is to perform close visual inspection of wing surfaces, leading edges, engine inlets, and other coop::,nents of the aircraft that are in view either £ran the oockpit or cabin (whichever provides maximum view}. If surfaces have oot been treated with FPD fluid, evidence of melting snow and possible freezing is sought. Also evidence of any ice formation that may have been induced by taxi operations is sought. Ii the aircraft has been treated with FPD fluids, evidence of a glossy snooth and wet surface is sought. If, as a result of these inspections, evidence of ice, snow, or frost formations is observed, the aircraft should be returned to a maintenance area for additional deicing.
(B) The fact that it is impractical for an aircraft crewmember to disanbark at the end of a runway and perform pretakeoff inspections, means that the crewmember should perform that inspection from the best vantage p::>int available fran within the aircraft. The crewmember may elect to q:,en windows, doors, or hatches to improve the view, but in many aircraft even this is impractical. In the darkness of night the crewmember nust rely l.lfX)n wing and Par 5 6
other aircraft illumination lights that ma.y oot provide sufficient reflection to make appropriate visual observations. The crewmember ma.y, where practical, call upon the assistance of qualified ground personnel. If under any circumstance, the pilot in carmand cannot ascertain that the aircraft is clean, takeoff should not be attempted.
(C) Conducting pretakeoff inspection in the ma.nner described relies upon the pilot in camiand to be knowledgeable of ground deicing procedures, that the ground deicing process was conducted in a thorough and unifoi::m ma.nner, and that critical surfaces or can.ponents oot in view during pretakeoff inspection will also be clean. The decision to takeoff, following pretakeoff inspection remains the responsibility of the pilot in ccmnan.d.
(ii) Rotorcraft.
(A) Only rotorcraft that have been certificated for flight in 1c1ng conditions should be operated in conditions conducive to icing such as freezing fog. To date oone have been so certificated by the FAA.
(B) Rotorcraft certificated for flight in falling and blowing snow ma.y operate in such conditions. In this case pretakeoff inspection of rotor systems should be conducted just prior to starting rotors turning. Rotor systems should oot be started unless blade surfaces and other critical canponents are free of ice, frost or oohering snow.
b. Ccmoon practices or suggested practices necessary to assure the pilot has every advantage for his judgements:
(1) Establish training programs to continually update pilots on the hazards of winter operations, adverse effects of ice formations on aircraft perfoi::mance and flight characteristics, proper use of ice protection equipnent, ground deicing and anti-icing procedures, and preflight and pretakeoff inspection procedures following ground deicing or anti-icing and operations in conditions conducive to aircraft icing.
(2) Establish training programs for ma.intenance or other personnel who perfotm aircraft deicing to assure thorough knowledge of the ooverse effects of ice formations on aircraft performance and flight characteristics, critical canp:>nents and specific ground deicing and anti-icing procedures for each aircraft type, and the use of ground deicing and anti-icing equipnent including detection of abnormal operational conditions.
(3) Establish quality assurance programs to assure that FPD fluids being p.irchased and used are of the proper characteristics, that proper ground deicing and anti-icing procedures are utilized, that all critical areas are inspected, and that all critical cnnponents of the aircraft are clean prior to departure.
(4) Perfoi::m thorough planning of ground deicing activities to assure that proper supplies and equipnent are available for forecast weather conditions and that responsibilities are specifically assigned and understcx:rl. This is to include ma.intenance service contracts.
Par 5 7
12/17/82AC 20-117
(5) Monitor weather oonditions very closely to assure that planning information remains valid during the ground deicing or anti-icing process and subsequent aircraft operations. FPD fluids, deicing or anti-icing procedures and departure plans should be altered acoordingly.
(6) Use FPD ooncentrations that will delay ice formations for as long a period as p::>ssible under the prevailing oonditions.
(7) Deice or anti-ice areas that may be viewed by the pilot (from inside the aircraft) first so that during pretakeoff inspection he may have assurance that other areas of the aircraft are clean since areas deiced or anti-iced first will generally freeze first.
(8) Use the two-stage deicing process where ice dep::>sits are first removed, and then all critical CX>JJp:>nents of the aircraft are ooated with an appropriate mixture of FPD fluid (anti-icing) to prolong effectiveness.
(9) Assure thorough ooordination of the ground deicing and anti-icing process so that final treatments are provided just prior to takeoff.
(10) Use remote sites near the take-off p::>sition, where feasible, for deicing or anti-icing to reduce the time between deicing and takeoff or to provide additional FPD fluid to prolong anti-icing effectiveness.
(11) Use multiple aircraft deicing or anti-icing units for faster and more uniform treatment during precipitation.
(12) Use FPO fluids that are approved for use by the aircraft manufacturer. sane fluids may not be compatible with aircraft materials and finishes and some may have dlaracteristics that impair aircraft performance and flight dlaracteristics or cause oontrol surface instabilities.
(13) Do not use substances that are approved for use on pneumatic bcx>ts (to improve deicing performance) for other prqx:>ses unless such uses are approved by the aircraft manufacturer.
c. Suggested practices for pilots to assure the clean aircraft ooncept.
(1) Be knowledgeable of the adverse effects of surface roughness on aircraft performance and flight dlaracteristics.
(2) Be knowledgeable of ground deicing and anti-icing practices and procedures being used on your aircraft whether this service is being performed by your own canpany, a service oontractor, or a fixed-base operator.
(3) Do not allow deicing or anti-icing until you are familiar with the ground deicing practices and quality oontrol procedures of the service organization.
(4) Be knowledgeable of critical areas of your aircraft and assure these areas are properly deiced and anti-iced, proper precautions are being taken during the deicing process to avoid damage to aircraft CX>JJp:>nents, and Par 5 8
'·.
12/ 17/82 AC 20-117 proper preflight inspections are performed even though this is also the resp::>nsibility of other organizations or personnel.
(5) Be knowledgeable of ice protection system function, capabilities, limitations, and q;>eration.
(6) Perform additional preflight inspections related to deicing or anti-icing as necessary or required.
(7) Be aware that no one can accurately determine the time of effectiveness of an FPD deicing or anti-icing treatment because of the many variables that can influence this time.
(8) Be knowledgeable of the variables that can reduce time of effectiveness and their general effects.
(9) Assure that deicing or the anti-icing treatment is performed at the last p::>ssible time prior to taxi to the takeoff p::>sition.
(10) Do not start engines, propellers, or rotor blades until it has been ascertained that all ice dep::>sits are rerroved. Ice particles shed fran rotating canponents under centrifugal and aerodynamic forces can be lethal.
(11) Be aware that certain q;>erations may produce recirculation of ice crystals, snow or rroisture.
(12) Be aware that q;>erations in close proximity to other aircraft can induce snow, other ice particles, or rroisture to be blown onto critical aircraft canponents, or allow dry snow to rrelt and refreeze.
(13) Do not takeoff if snow or slush is observed splashing onto critical areas of the aircraft, such as wing leading edges, during taxi.
(14) Always perform pretakeoff inspections just prior to takeoff.
(15) Do not takeoff if p::>sitive evidence of a clean aircraft cannot be ascertained.
Director of Airworthiness, AWS-1 Par 5 9
AC 20-11712/17/82 Appendix 1 .APPENDIX 1. RELA1'EO FAA PUBLIC1(J.1I00S, TRAINIOO MATERIAL, .AND Ol'HER READIOO MM"ERIAL
1. REI.Ja'ED FAA PUBLICATIOOS.
-- Air Carrier Operations Bulletin (llC:OB), No. 7-81-1, Aircraft Deicing and Anti-Icing Procedures, dated April 10, 1981, ror/FAAOrder 8430.17, Change 21.
- N:OB, No. 7-76-9, Aircraft Control and Lifting Surfaces-cold weather Operations, October 20, 1976.
-- N:OB, No. 7-76-11, Engine Ice Accumulation - Ground Idle (Formerly Air Carrier Operations Alert, No. 70-9), October 20, 1976.
-- N:OB, No. 7-76-12, Turbojet Aircraft Engine Icing During Prolonged Ground Operations in Icing Conditions (Formerly Air Carrier Operations Alert No. 69-3), October 20, 1976.
-- Kll3, No. 7-76-13, Takeoff warning Systems During Cold weather Operations, October 20, 1976.
-- N:OB, No. 7-76-2, water/Snow Entering Parked Boeing 727 Aircraft Causing Electrical Fewer wss, October 20, 1976.
-- ACOB, No. 7-76-1, Winter Operations Under FAR 121 and 127 (Formerly Air Carrier Operations Bulletin No. 68-15), October 20, 1976.
-- Air Carrier Operations Alert (JICOA), No. 67-3, Aircraft Control and Lift Surfaces - Cold weather Operations.
-- KJJA No. 69-3, Turbojet Aircraft Engine Icing During Prolonged Ground Operations in Icing Conditions.
-- JICOA No. 70-9, Engine Ice Accumulation - Ground Idle.
--Air Carrier Maintenance Bulletin (J.\CMB) No. 115, Deicing of Aircraft with Engines Operating.
-- .1CMB 127, Aircraft Deicer Fluids.
-- .ACMB 128, Responsibility for Aircraft Servicing.
-- .ACMB 155, Winter Operation of Aircraft.
-- IC 00-6A, Aviation Weather, March 3, 1975.
-- IC 00-458, Aviation Weather Services, 1979.
-- IC 20-73, Aircraft Ice Protection, 11;>ril 21, 1971.
-- IC 20-93, Flutter Due to Ice or Foreign Substance On Or In Aircraft Control Surfaces, January 29, 1976.
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12/ 17/82AC 20-117 Appendix 1
- JtC 20-113, Pilot Precautions and procedures to l:::le taken in Preventing Aircraft Reciprocating Engine Induction System & Fuel System Icing Problems, Oct. 22, 1981.
-- JtC 20-106, Aircraft Inspection for the General Aviation Aircraft Owner, April 1978.
- JtC 61-84A, '!he Role of Preflight Preparation, December 1, 1980.
-- JtC 91-6A, water, Slush, and Snow on the Runway, May 24, 1978.
-- JtC 91-13C, Cold weather Operation of Aircraft, July 24, 1979.
-- JtC 91-51, Airplane Deice and Anti-Ice Systems, September 15, 1977.
-- 11C 135-9, FAR Part 135 Icing Limitations, May 30, 1981.
-- JtC 121-12, Wet or Sli~ry R.Jnways, August 17, 1967.
-- JtC 150/5380-4, Ranp Operations During Perioos of Ice and Snow Accumulations, September 11, 1968.
-- FAA RD-80-50, Engine Inlet Anti-Icing System Evaluation Procedure (Report).
-- M:;F 140-75-3, Report of Propulsion Conference and Environmental Workshop.
-- Aircraft Ice Protection, Report of Synposium, Jpril 28-30, 1969.
-- FAA General Aviation News Article "Rime Without Reason."
-- FAA Pamphlet ''Weather (Pilot's) How It Is Forecast."
-- FAA Pamphlet "'!be Weather Decision."
2. TRAINING MATERIAL.
-- 11C 61-80, Instrument Rating, Written Test Guide.
-- JtC 61-18B, Air Transport Pilot (Airplane, written test guide).
-- 11C 61-21A, Flight Training Handbook.
-- 11C 61-23B, Pilots Handbook of Aeronautical Knowledge.
-- 11C 61-31B, Gyroplane Pilot Written Test Guide, Private and COllll\ercial.
-- 11C 61-70A, Flight Instructor, Instrument Airplane, Written Test Guide.
-- JtC 61-71B, Catrnercial Pilot - Airplane - Written Test Guide.
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