Appendix F F-5 F.6.2 Navigation Data Displays. Navigation data, including a TO/FROM indication and a failure indicator, must be displayed on a lateral deviation display (course deviation indicator (CDI), electronic horizontal-situation indicator (EHSI)) and/or a navigation map display. These must be used as primary flight instruments for the navigation of the aircraft, for maneuver anticipation and for failure/status/integrity indication. A non-numeric lateral deviation display (e.g., CDI, EHSI), with a TO/FROM indication and a failure annunciation, for use as primary flight instruments for navigation of the aircraft, for maneuver anticipation, and for failure/status/integrity indication, should have the following attributes:
1. The displays must be visible to the pilot and located in the primary field of view (FOV).
2. The lateral deviation display scaling must agree with any alerting and annunciation limits.
3. The lateral deviation display must have a full-scale deflection suitable for the current phase of flight.
Note: This does not apply for installations where an electronic map display contains a graphical display of the flightpath and path deviation.
4. The display scaling may be set automatically by default logic; automatically to a value from a navigation database; or manually by flightcrew procedures.
The full-scale deflection value must be known or must be available for display to the pilot commensurate with the required track-keeping accuracy.
5. The lateral deviation display must be automatically slaved to the RNP-computed path. It is recommended that the course selector of the deviation display be automatically slewed to the RNP-computed path.
Note: This does not apply for installations where an electronic map display contains a graphical display of the flightpath and path deviation.
6. As an alternate means, a navigation map display must give equivalent functionality to a lateral deviation display with appropriate map scales (scaling may be set manually by the pilot). To be approved as an alternative means, the navigation map display must be shown to meet the TSE requirements and be located in the primary FOV.
7. It is not necessary for navigation displays, particularly primary flight displays (PFD), to include an Actual Navigation Performance (ANP) or RNP value.
The displays only need to provide an alert if the RNP for the operation cannot be met.
F.6.3 System Capabilities. The following system capabilities are required as a minimum within any RNP 4 equipment:
1. The capability to continuously display to the pilot flying (PF), on the primary flight instruments for navigation of the aircraft (primary navigation display),
Appendix F F-6 the RNP-computed desired path and aircraft position relative to the path. For operations where the required minimum flightcrew is two pilots, a means for the pilot monitoring (PM) to verify the desired path and the aircraft position relative to the path must also be provided.
2. A navigation database, containing current navigation data officially promulgated for civil aviation, which can be updated in accordance with the Aeronautical Information Regulation and Control (AIRAC) cycle. The stored resolution of the data must be sufficient to achieve the required track-keeping accuracy. The database must be protected against pilot modification of the stored data.
3. The means to display the validity period of the navigation data to the pilot.
4. The means to retrieve and display data stored in the navigation database relating to individual waypoints and navigation aids, to enable the pilot to verify the route to be flown.
5. A means for the crew to create, review, and activate a flight plan. The system must incorporate a means for the crew to verify flight plan entries or changes before they are activated. The guidance output must not be affected until the flight plan or flight plan changes are activated.
6. The means to display the following items, either in the pilot’s primary FOV, or on a readily accessible display page:
• The active navigation sensor type,
• The identification of the active (To) waypoint,
• The ground speed or time to the active (To) waypoint, and
• The distance and bearing to the active (To) waypoint.
7. The capability to execute a “direct to” function.
8. The system must have the capability to automatically execute leg transitions and maintain tracks consistent with the following Aeronautical Radio, Inc.
(ARINC) Specification 424 path terminators:
• Course to Fix (CF),
• Direct to Fix (DF), and
• Track to Fix (TF).
Note: Path terminators are defined in ARINC Specification 424, and their application is described in more detail in RTCA documents, DO-236( ) and DO-201( ).
9. When executing a parallel offset (Appendix I, Additional Capabilities), the capability to execute parallel tracks at a selected offset distance. When executing a parallel offset (Appendix I), the RNP value and all performance
Appendix F F-7 criteria of the original route in the active flight plan must be applicable to the offset route.
• The system must provide for entry of offset distances in increments of 1 NM, left or right of course. The system must be capable of offsets of at least 20 NM.
• System offset mode operation must be clearly indicated to the pilot. When in offset mode, the system must provide reference parameters (e.g., cross-track (XTK) deviation, distance-to-go, time-to-go) relative to the offset path and offset reference points.
• An offset must not be propagated through route discontinuities, unreasonable path geometries, or beyond the initial approach fix (IAF).
• The system must provide an annunciation prior to the end of the offset path, with sufficient time to return to the original path.
• Once a parallel offset (Appendix I) is activated, the offset must remain active for all flight plan route segments until removed automatically, until the pilot enters a direct-to routing, or until pilot (manual) cancellation.
• The parallel offset (Appendix I) function must be available for en route TF and the geodesic portion of DF leg types.
Note: Systems compliant with parallel offset (Appendix I) requirements in RTCA/DO-229C (or later revision), DO-236C (or later revision) or DO-283A (or later revision) meet the parallel offset criteria for RNP 4.
10. For RNP 4 tracks in oceanic/remote continental airspace using flexible
(e.g., organized) tracks, a means to enter the unique waypoints required to build a track assigned by the Air Traffic Service (ATS) provider. Manual entry or creation of new waypoints is permitted, by manual entry of latitude and longitude.
11. The capability for automatic leg sequencing with display to the pilots.
12. The capability to automatically sequence fixes.
13. The capability to display an indication of the RNP 4 system failure in the pilot’s primary FOV.
14. The capability to indicate to the crew when the NSE alert limit is exceeded
(i.e., the alert provided by the onboard performance monitoring and alerting function).
15. The system must have the capability to perform flyby transitions:
• Flyby transitions must be the default when a transition type is not specified,
• Navigation systems should be designed to keep aircraft within the theoretical transition area, and
Appendix F F-8
• Flyby theoretical transition areas are based upon the following assumptions:
1. Course changes do not exceed 120 degrees for low altitude transitions (aircraft barometric altitude is less than flight level (FL) 195), and
2. Course changes do not exceed 70 degrees for high altitude transitions (aircraft barometric altitude is equal to or greater than FL 195).
Note: Systems compliant with the flyby transition requirements in RTCA/DO-236C (or later revision), or DO-283A (or later revision) meet the flyby transition criteria for RNP 4.
F.6.4 Database Integrity. The operator must ensure their navigation database supplier possesses a Type 2 Letter of Acceptance (LOA) in accordance with AC 20-153( ), Acceptance of Aeronautical Data Processes and Associated Databases.
F.6.5 Path Terminators. The database supplier should not substitute path terminators in lieu of those specified in the original State AIP data.
F.7 Operational Requirements.
F.7.1 Navigation Equipage. All RNP 4 operations in oceanic and remote continental areas must have at least dual independent LRNSs of integrity such that the navigation system does not provide misleading information.
F.7.2 Aircraft Incorporating GPS. Aircraft equipped with GPS avionics by one of the following three methods is acceptable for receiving an RNP 4 operational approval:
1. Federal Aviation Administration (FAA) responsible Aircraft Certification Service office (or U.S. Military equivalent) letter meeting performance requirements of FAA N 8110.60, GPS as a Primary Means of Navigation for Oceanic/Remote Operations, canceled December 4, 1996.
2. FAA responsible Aircraft Certification Service office (or U.S. Military equivalent) letter meeting performance requirements of AC 20-138( ).
3. GPS avionics marked with TSO-C129( )/TSO-C145( )/TSO-C146( )/ TSO-C196( ) and installed in accordance with AC 20-138( ).
F.7.2.1 The equipment configuration used to demonstrate the required accuracy must be supportable in RNP 4 oceanic and remote continental airspace. For example, the statistical benefit of estimating position using INS position data filtered with distance measuring equipment (DME) data will not be considered.
F.7.2.2 The equipment configuration used to demonstrate the required accuracy must be identical to the configuration, which is specified in the minimum equipment list (MEL).
Appendix F F-9 F.7.3 Aircraft Qualification Documentation. The aircraft or avionics manufacturers should develop aircraft qualification documentation that shows compliance with the applicable criteria, as appropriate. For aircraft without approval to fly RNP 4 operations, the aircraft or avionics manufacturers should develop RNP 4 qualification documentation showing compliance with this appendix provided equipment is properly installed and operated.
The necessary documentation should also define the recommended RNP maintenance procedures. This is not required for aircraft with an AFM or AFMS which explicitly states that the RNP system is approved for instrument flight rules (IFR) operations with RNP values at least as low as RNP 4 and the equipment meets the performance and reliability guidance of AC 20-138( ).
F.7.3.1 Prior to application, operators and manufacturers of their equipment should review all performance requirements. Installation of equipment by itself does not guarantee operational approval or permit operational use.
F.8 Operational Considerations.
F.8.1 Pilot Training and Qualification. Operators should ensure pilots are trained and qualified to operate in RNP 4 airspace.
F.8.2 Preflight. The following actions should be completed during preflight:
1. Review maintenance logs and forms to ascertain the condition of equipment required for flight in RNP 4 airspace or on an RNP 4 route, and
2. Ensure that maintenance action has been taken to correct defects to required equipment.
F.8.2.1 At dispatch or during flight planning, the operator must ensure that adequate navigation capability is available en route to enable the aircraft to navigate to RNP 4 and include the availability of FDE, if appropriate for the operation.
Note: When the predicted loss of FDE exceeds 25 minutes, then RNP 4 operations are not available, and the operator must reschedule the flight.
F.8.3 General In-Flight Considerations. For flexible route structures, manual entry of waypoints (i.e., latitude and longitude) may be permitted provided the potential for entry error by pilots is mitigated by adequate flightcrew procedures. The manual entry or creation of new waypoints, by manual entry of latitude and longitude or rho/theta values for fixed, published routes is not permitted. The pilot may modify the route through the insertion or deletion of specific waypoints in response to air traffic control (ATC) clearances. Pilots must not change any database waypoint type from a flyby to a flyover or vice versa.
F.8.3.1 The pilot must confirm the correct route is loaded. This process includes confirmation of the waypoint sequence, reasonableness of track angles and distances, and any other parameters that can be altered by the pilot, such as
Appendix F F-10 altitude or speed constraints. A navigation system textual display or navigation map display must be used.
Note: Flightcrew may notice a slight difference between the navigation information portrayed on the chart and their primary navigation display. Differences of 3 degrees or less may result from equipment manufacturer’s application of magnetic variation and are operationally acceptable.
F.8.3.2 For RNP 4 operations, pilots must use a lateral deviation indicator, flight director (FD), or autopilot (AP) in lateral navigation (LNAV) mode. Pilots of aircraft with a lateral deviation display must ensure lateral deviation scaling is suitable for RNP 4 operations.
F.8.3.3 At least two independent LRNS capable of navigating to the RNP should be operational at the oceanic entry point. If this is not the case, the pilot should consider an alternate routing or divert for repairs.
F.8.3.4 If the navigation system does not automatically retrieve and set RNP 4 from the onboard navigation database for the entirety of the RNP 4 operation, the flightcrew’s operating procedures must manually set RNP 4. This ensures proper RNP system monitoring and alerting is available for the RNP 4 operation.
F.8.3.5 Operator in-flight procedures must include verifying the RNP value set in the FMS matches the equipment capability and authorizations as annotated in the flight plan prior to entering oceanic and remote continental airspace.
F.8.3.6 Operator in-flight operating procedures must include mandatory cross-checking procedures to identify navigation errors in sufficient time to prevent aircraft from an inadvertent deviation from ATC-cleared routes.
F.8.3.7 Crews must advise ATC of any deterioration or failure of the navigation equipment below the navigation performance requirements or of any deviations required for a contingency procedure.
F.8.3.8 All pilots are expected to maintain centerline, as depicted by onboard lateral deviation indicators and/or flight guidance during all RNP operations described in this AC unless authorized to deviate by ATC (such as Strategic Lateral Offset Procedure (SLOP)) or under emergency conditions.
For normal operations, XTK error/deviation (the difference between the displayed path and the displayed aircraft position relative to the displayed path, (i.e., FTE)) should be limited to half the RNP value associated with the procedure (i.e., 2 NM for RNP 4). Brief deviations from this standard
(e.g., overshoots or undershoots) during and immediately after turns, up to a maximum of one times the RNP value (i.e., 4 NM for RNP 4), are allowable.
Appendix F F-11 Note: Some aircraft do not display or compute a path during flyby turns. As such, pilots of these aircraft may not be able to adhere to half the lateral navigation accuracy during turns but are still expected to satisfy the standard during intercepts following turns and on straight segments. This does not apply to the execution of fixed radius transition (FRT) procedures.
F.8.3.9 Operational qualification for RNP routes requires flightcrew monitoring of lateral and, if installed, vertical deviations on the pilot’s PFDs to ensure the aircraft remains within the bounds defined by the route. The deviation must be monitored, and action taken to minimize errors during all RNP operations.
F.8.3.10 The flightcrew must be able to assess the impact of equipment failure on the anticipated RNP operation and take appropriate action.
F.8.3.11 In addition to normal operating procedures, prior to commencing the procedure the flightcrew should accomplish the following:
1. For multisensor systems, crews must verify that the correct sensor is being used for position computation; and
2. Where Controller-Pilot Data Link Communication (CPDLC) is used to uplink flight plan changes for routing that is not contained in the navigation database, the flightcrew should confirm the RNP in effect matches the airspace requirement. If not, the flightcrew should manually enter the RNP applicable to the route.
F.8.3.12 Emergency procedures for operations in RNP 4 airspace or on RNP 4 routes are no different than normal oceanic emergency procedures with one exception, crews must be able to recognize and ATC must be advised when the aircraft is no longer able to navigate to its RNP 4 approved capability.
Appendix G G-1 APPENDIX G. QUALIFICATION CRITERIA FOR REQUIRED NAVIGATION PERFORMANCE (RNP) 10 OCEANIC AND REMOTE CONTINENTAL OPERATIONS G.1 Introduction. This appendix provides guidance for operation in and is intended to support 50 nautical miles (NM) lateral and the 50 NM longitudinal distance based separation minima. Previous authorizations in accordance with Federal Aviation Administration (FAA) Order 8400.12C, Required Navigation Performance 10 (RNP 10) Operational Authorization, remain valid. This appendix does not address communications or surveillance requirements that may be specified to operate on a particular route or in a particular area. Those requirements are specified in other documents, such as the Aeronautical Information Publications (AIP) and the International Civil Aviation Organization (ICAO) Doc 7030, Regional Supplementary Procedures (SUPPS) and ICAO Doc 4444 PANS ATM, Procedures for Air Navigation Services, Air Traffic Management.
Note: Area Navigation (RNAV) 10 is designated and authorized as RNP 10. This document uses the designation of RNP 10.
G.2 Aircraft and System Requirements for RNP 10.
G.2.1 Statement of Compliance (SOC). Aircraft with an SOC with RNP 10 criteria in Advisory Circular (AC) 20-138( ), Airworthiness Approval of Positioning and Navigation Systems, in their Airplane Flight Manual (AFM), Airplane Flight Manual Supplement (AFMS), pilot’s operating handbook (POH), or the operating manual for their avionics meet the performance and functional requirements of this appendix. RNP compliance is documented in the AFM and is typically not limited to RNP 10. The AFM will address RNP, navigation specifications (Nav Specs) that have been demonstrated and any related provisions applicable to its use (e.g., Navigational Aid (NAVAID) sensor requirements).
G.2.2 Equipment. Aircraft must be equipped with at least dual navigation systems except for operation in the Gulf of Mexico (GOMEX) where Single Long-Range Navigation System (S-LRNS) RNP 10 is authorized.
G.3 System Performance.
G.3.1 Accuracy. During operations in airspace or on routes designated as RNP 10, the lateral Total System Error (TSE) must be within ±10 NM for at least 95 percent of the total flight time. The along-track (ATRK) error must also be within ±10 NM for at least 95 percent of the total flight time.
Note: For RNP 10 approval, navigation positioning error is considered the dominant contributor to cross-track (XTK) and ATRK for aircraft capable of coupling the navigation system to the flight director (FD) or autopilot (AP).
Flight Technical Error (FTE), Path Definition Error (PDE), and display error are considered to be insignificant for the purposes of RNP 10 approval (RNP 10 is intended for oceanic and remote continental areas where aircraft separation minima of 50 NM are applied).
Appendix G G-2 G.3.2 Integrity. Malfunction of the aircraft’s long-range navigation (LRN) equipment without annunciation is a major failure condition (i.e., the probability of a malfunction with no annunciation must be less than 10-5 per hour).
G.3.3 Continuity. Loss of function of the LRN equipment is a major failure condition for oceanic and remote continental operations. Dual independent long-range navigation system (LRNS) equipage may satisfy the continuity criteria (excluding Signal in Space (SIS) criteria).
G.3.4 SIS. If using Global Navigation Satellite System (GNSS), the aircraft LRN equipment must provide an alert if the probability of SIS errors causing a lateral position error greater than 20 NM exceeds 10-7 per hour.
G.4 Aircraft Eligibility.
G.4.1 Prior Navigation System Certification. Aircraft Original Equipment Manufacturers (OEM) and operators may use a prior navigation system certification to recognize an aircraft whose performance under the criteria of another RNP specification equates to or exceeds the RNP 10 performance criteria listed in AC 20-138( ). Aircraft OEMs and operators may also use other Nav Spec standards when they are sufficient to ensure compliance with RNP 10 performance criteria.
Note: Qualification through data collection guidance provided in Order 8400.12C is available in a booklet format online. Operators qualifying by the data collection methods should contact their Principal Operations Inspector (POI) and download a copy of the booklet, RNP 10 Qualification through Data Collection from the Flight Technologies and Procedures Division web page at www.faa.gov/about/offi ce_org/headquarters_offices/avs/offices/afx/afs/afs400/, Performance Based Flight Systems Branch, Oceanic and Remote Airspace (Special Areas of Operations).
G.4.2 Application Description. RNP 10 is an RNAV operational application supporting 50 NM lateral and 50 NM longitudinal distance-based aircraft separation minima in oceanic or remote continental airspace. As an RNAV application, there is no requirement for onboard performance monitoring and alerting. There are two methods to recognize aircraft and system eligibility for RNP 10 operations: 1) RNP 10 certification; and,
2) prior navigation system certification.
G.4.3 Eligibility Through an RNP 10 Certification. RNP 10 compliance is documented in the AFM and is typically not limited to RNP 10. The AFM/AFMS should document the demonstrated RNP values the aircraft supports along with any limitations
(e.g., navigation aid sensor requirements for present position updating).
Note: Aircraft qualified for RNP 4 operations automatically qualify for RNP 10 operations.
G.4.3.1 An aircraft may have an airworthiness approval specific to RNP 10 qualification. The following (or equivalent) is an example of AFM wording
Appendix G G-3 when RNP 10 approvals are granted for either a change in, or new demonstration of, the inertial navigation system (INS)/Inertial Reference Unit (IRU)-certified performance:
“The XXX navigation system meets the aircraft qualification criteria of AC 20-138( ), as a primary means of navigation for flights up to XXX hours in duration without present position updating. The determination of flight duration starts when the flightcrew places the long-range navigation system in the inertial navigation mode,” Note: The “XXX hours” specified in the AFM/AFMS for INS/IRU systems do not include credit for present position updating.
G.4.3.2 For LRNSs capable of updating the aircraft’s present position while airborne, the airworthiness approval must address the impact present position updating has on position accuracy and any impact on time limits for RNP 10 operations. The approval should clarify the role of ground-based navigation facilities in present position updating (if any), clarify the role of GNSS present position updating (if equipped), and define any requisite flightcrew procedures necessary to initiate and terminate present position updating. The credit received for present position updating can be applied to the “XXX hours” specified in the AFM/AFMS for INS/IRU systems.
G.4.3.3 Demonstration of aircraft performance in accordance with AC 20-138( ) does not constitute operations approval to conduct RNP operations.
G.4.3.4 The demonstration of inertial performance to FAA Aircraft Certification Service (AIR) forms the basis for the suggested AFM/AFMS wording above, but is only one element of the approval process. Aircraft that have this wording in their flight manual will be eligible for operational approval through issuance of operations specifications (OpSpecs)/management specifications (MSpecs) or a Letter of Authorization (LOA) (as applicable) when the operator and aircraft meet all other RNP 10 qualification criteria.
G.5 Aircraft Equipped with Two or More INS or IRUs. Inertial systems approved in accordance with Title 14 of the Code of Federal Regulations (14 CFR) part 121, Appendix G are considered to meet RNP 10 requirements for up to 6.2 hours of flight time. This time starts when the system is placed in the inertial navigation mode.
G.5.1 INS/IRU System Updates. If the flightcrew updates the INS/IRU systems en route (through manual or automatic means), the flightcrew must adjust the 6.2 hour RNP 10 time limit to account for the update’s accuracy. The flightcrew must base any adjustments to the time limit on the demonstrated capability of the updates stated in the aircraft’s airworthiness approval documentation (i.e., the AFM/AFMS).
G.5.1.1 INS/IRU accuracy, reliability, training, and maintenance issues required by an airworthiness approval in compliance with part 121, Appendix G are applicable to an RNP 10 operation, including any associated procedures
Appendix G G-4 in oceanic and remote continental airspace. Except as authorized by the FAA Administrator, and in accordance with the applicable section of 14 CFR, RNP 10 operations based solely IRS/IRU requires at least dual equipage
(i.e., two or more inertial systems). Refer to 14 CFR part 121, § 121.351, part 125, § 125.203, and part 135, § 135.165.
Note: The long-term inertial drift rate of 2.0 NM/hour (a 95 percent radial position error rate (circular error rate)) is the performance basis for the 6.2 hour time limit. This drift rate is statistically equivalent to an individual 95 percent XTK and an individual 95 percent ATRK position error rates (orthogonal error rates) of 1.6015 NM/hour each;
and, a 95 percent XTK and a 95 percent ATRK position error limit of 10 NM each (e.g., 10 NM/1.6015 NM/hour = 6.2 hours).
G.5.1.2 Aircraft approved for North Atlantic Minimum Navigation Performance Specifications (NAT/MNPS) or Australian RNAV operations meet RNP 10 criteria for up to 6.2 hours after the flightcrew places the LRNS in the inertial navigation mode.
G.5.2 Two or More INSs or IRUs – Extended Time Limit. The 6.2 hour time limit is the baseline for RNP 10 inertial systems performance, and the time limit begins when the flightcrew places the LRNS in the inertial navigation mode. However, this time limit may be extended by one of the following methods:
1. Establishing an extended time limit during a formal RNP 10 airworthiness approval process (e.g., a new type certificate (TC), amended TC, or Supplemental Type Certificate (STC) project);
2. An existing airworthiness approval holder requests an extension for the installed inertial navigation system from the responsible Aircraft Certification Service office based on justifying engineering data; or
3. An airworthiness applicant or existing airworthiness approval holder requests an extended time limit by showing how multiple navigation sensors that mix or average navigation position error justifies an extension (e.g., triple-mixed INSs). If the applicant requests an extended time limit based on mixing, then the availability of the mixing capability is a limitation for flight on RNP 10 routes. If the mixing or averaging function is not available, the operator must use a time limit that does not depend on mixing.
G.6 Route Evaluation For RNP 10 Time Limits For Aircraft Equipped Only With INS or IRU. An RNP 10 time limit must be established for aircraft equipped only with INS or IRU. When planning operations in areas where RNP 10 is applied, the operator must establish that the aircraft will comply with the time limitation on the routes that it intends to fly.
G.6.1 Time Limit Considerations. In making this evaluation, the operator must consider the effect of head winds and, for aircraft not capable of coupling the navigation system or
Appendix G G-5 FD to the AP, the operator may choose to make this evaluation on a one-time basis or on a per-flight-basis. The operator should consider the points listed in the following subsections in making this evaluation.
1. Route Evaluation. The operator must establish the capability of the aircraft to satisfy the RNP 10 time limit established for dispatch or departure into RNP 10 airspace.
2. Start Point for Calculation. The calculation must start at the point where the system is placed in navigation mode or the last point at which the system is expected to be updated.
3. Stop Point for Calculation. The stop point may be one of the following:
• The point at which the aircraft will begin to navigate by reference to ICAO standard NAVAIDs (very high frequency omni-directional range (VOR), distance measuring equipment (DME), Non-Directional Beacon (NDB)) and/or comes under Air Traffic Service (ATS) surveillance; or
• The first point at which the navigation system is expected to be updated.
4. Sources of Wind Component Data. The head wind component to be considered for the route may be obtained from any source found acceptable to the FAA. Acceptable sources for wind data include:
• The National Weather Service (NWS),
• Industry sources (e.g., Boeing Winds on World Air Routes), and
• Historical airline data supplied by the operator.
G.6.2 One-Time Calculation Based on 75 Percent Probability Wind Components. Certain sources of wind data establish the probability of experiencing a given wind component on routes between city pairs on an annual basis. If an operator chooses to make a one-time calculation of RNP 10 time limit compliance, he/she may use the annual 75 percent probability level to calculate the effect of head winds. This level has been found to be a reasonable estimation of wind components.
G.6.3 Calculation of Time Limit for Each Specific Flight. The operator may choose to evaluate each individual flight using flight-planned winds to determine if the aircraft will comply with the specified time limit. If it is determined that the flight will exceed the time limit, then the aircraft must fly an alternate route or delay the flight until it can meet the time limit. This evaluation should be considered a flight planning or dispatch task.