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Chapter 8. Medical Facts for Pilots Section 1. Fitness for Flight 8-1-1. Fitness For Flight 8-1-1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-1-2. Effects of Altitude 8-1-3 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-1-3. Hyperventilation in Flight 8-1-4 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-1-4. Carbon Monoxide Poisoning in Flight 8-1-5 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-1-5. Illusions in Flight 8-1-5 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-1-6. Vision in Flight 8-1-6 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-1-7. Aerobatic Flight 8-1-7 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-1-8. Judgment Aspects of Collision Avoidance 8-1-8 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Chapter 9. Aeronautical Charts and Related Publications Section 1. Types of Charts Available 9-1-1. General 9-1-1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-1-2. Obtaining Aeronautical Charts 9-1-1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-1-3. Selected Charts and Products Available 9-1-1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-1-4. General Description of each Chart Series 9-1-1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-1-5. Where and How to Get Charts of Foreign Areas 9-1-12 . . . . . . . . . . . . . . . . . . . . . . . . . Chapter 10. Helicopter Operations Section 1. Helicopter IFR Operations 10-1-1. Helicopter Flight Control Systems 10-1-1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-1-2. Helicopter Instrument Approaches 10-1-3 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-1-3. Helicopter Approach Procedures to VFR Heliports 10-1-5 . . . . . . . . . . . . . . . . . . . . . . 10-1-4. The Gulf of Mexico Grid System 10-1-6 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Section 2. Special Operations 10-2-1. Offshore Helicopter Operations 10-2-1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-2-2. Helicopter Night VFR Operations 10-2-7 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-2-3. Landing Zone Safety 10-2-10 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-2-4. Emergency Medical Service (EMS) Multiple Helicopter Operations 10-2-16 . . . . . . . . Appendices Appendix 1. Bird/Other Wildlife Strike Report Appendix 1-1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Appendix 2. Volcanic Activity Reporting Form (VAR) Appendix 2-1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . Appendix 3. Laser Beam Exposure Questionnaire Appendix 3-1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Appendix 4. Abbreviations/Acronyms Appendix 4-1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Pilot/Controller Glossary PCG-1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Index I-1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3/15/07 7110.65R CHG 2 AIM 7/31/08 AIM 2/14/08 1-1-1 Navigation Aids

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Chapter 1. Air Navigation Section 1. Navigation Aids 1-1-1. General a. Various types of air navigation aids are in use today, each serving a special purpose. These aids have varied owners and operators, namely: the Federal Aviation Administration (FAA), the military ser- vices, private organizations, individual states and foreign governments. The FAA has the statutory authority to establish, operate, maintain air naviga- tion facilities and to prescribe standards for the operation of any of these aids which are used for instrument flight in federally controlled airspace. These aids are tabulated in the Airport/Facility Directory (A/FD). b. Pilots should be aware of the possibility of momentary erroneous indications on cockpit displays when the primary signal generator for a groundbased navigational transmitter (for example, a glideslope, VOR, or nondirectional beacon) is inoperative. Pilots should disregard any navigation indication, regardless of its apparent validity, if the particular transmitter was identified by NOTAM or otherwise as unusable or inoperative. 1-1-2. Nondirectional Radio Beacon (NDB) a. A low or medium frequency radio beacon transmits nondirectional signals whereby the pilot of an aircraft properly equipped can determine bearings and “home” on the station. These facilities normally operate in a frequency band of 190 to 535 kilohertz (kHz), according to ICAO Annex 10 the frequency range for NDBs is between 190 and 1750 kHz, and transmit a continuous carrier with either 400 or 1020_hertz (Hz) modulation. All radio beacons except the compass locators transmit a continuous three-letter identification in code except during voice transmissions. b. When a radio beacon is used in conjunction with the Instrument Landing System markers, it is called a Compass Locator. c. Voice transmissions are made on radio beacons unless the letter “W” (without voice) is included in the class designator (HW). d. Radio beacons are subject to disturbances that may result in erroneous bearing information. Such disturbances result from such factors as lightning, precipitation static, etc. At night, radio beacons are vulnerable to interference from distant stations. Nearly all disturbances which affect the Automatic Direction Finder (ADF) bearing also affect the facility's identification. Noisy identification usually occurs when the ADF needle is erratic. Voice, music or erroneous identification may be heard when a steady false bearing is being displayed. Since ADF receivers do not have a “flag” to warn the pilot when erroneous bearing information is being displayed, the pilot should continuously monitor the NDB's identification. 1-1-3. VHF Omni-directional Range (VOR) a. VORs operate within the 108.0 to 117.95 MHz frequency band and have a power output necessary to provide coverage within their assigned operational service volume. They are subject to line-of-sight restrictions, and the range varies proportionally to the altitude of the receiving equipment. NOTE- Normal service ranges for the various classes of VORs are given in Navigational Aid (NAVAID) Service Volumes, paragraph 1-1-8.

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b. Most VORs are equipped for voice transmis- sion on the VOR frequency. VORs without voice capability are indicated by the letter “W” (without voice) included in the class designator (VORW). c. The only positive method of identifying a VOR is by its Morse Code identification or by the recorded automatic voice identification which is always indicated by use of the word “VOR” following the range's name. Reliance on determining the identifica- tion of an omnirange should never be placed on listening to voice transmissions by the Flight Service Station (FSS) (or approach control facility) involved. Many FSSs remotely operate several omniranges with different names. In some cases, none of the VORs have the name of the “parent” FSS. During AIM 2/14/08 1-1-2 Navigation Aids periods of maintenance, the facility may radiate a T-E-S-T code (-_______-) or the code may be removed. d. Voice identification has been added to numer- ous VORs. The transmission consists of a voice announcement, “AIRVILLE VOR” alternating with the usual Morse Code identification. e. The effectiveness of the VOR depends upon proper use and adjustment of both ground and airborne equipment. 1. Accuracy. The accuracy of course align- ment of the VOR is excellent, being generally plus or minus 1 degree. 2. Roughness. On some VORs, minor course roughness may be observed, evidenced by course needle or brief flag alarm activity (some receivers are more susceptible to these irregularities than others). At a few stations, usually in mountainous terrain, the pilot may occasionally observe a brief course needle oscillation, similar to the indication of “approaching station.” Pilots flying over unfamiliar routes are cautioned to be on the alert for these vagaries, and in particular, to use the “to/from” indicator to determine positive station passage. (a) Certain propeller revolutions per minute (RPM) settings or helicopter rotor speeds can cause the VOR Course Deviation Indicator to fluctuate as much as plus or minus six degrees. Slight changes to the RPM setting will normally smooth out this roughness. Pilots are urged to check for this modulation phenomenon prior to reporting a VOR station or aircraft equipment for unsatisfactory operation. 1-1-4. VOR Receiver Check a. The FAA VOR test facility (VOT) transmits a test signal which provides users a convenient means to determine the operational status and accuracy of a VOR receiver while on the ground where a VOT is located. The airborne use of VOT is permitted; however, its use is strictly limited to those areas/altitudes specifically authorized in the A/FD or appropriate supplement. b. To use the VOT service, tune in the VOT frequency on your VOR receiver. With the Course Deviation Indicator (CDI) centered, the omnibearing selector should read 0 degrees with the to/from indication showing “from” or the omnibearing selector should read 180 degrees with the to/from indication showing “to.” Should the VOR receiver operate an RMI (Radio Magnetic Indicator), it will indicate 180 degrees on any omni-bearing selector (OBS) setting. Two means of identification are used. One is a series of dots and the other is a continuous tone. Information concerning an individ- ual test signal can be obtained from the local FSS. c. Periodic VOR receiver calibration is most important. If a receiver's Automatic Gain Control or modulation circuit deteriorates, it is possible for it to display acceptable accuracy and sensitivity close into the VOR or VOT and display out-of-tolerance readings when located at greater distances where weaker signal areas exist. The likelihood of this deterioration varies between receivers, and is generally considered a function of time. The best assurance of having an accurate receiver is periodic calibration. Yearly intervals are recommended at which time an authorized repair facility should recalibrate the receiver to the manufacturer's specifications. d. Federal Aviation Regulations (14 CFR Section_91.171) provides for certain VOR equipment accuracy checks prior to flight under instrument flight rules. To comply with this requirement and to ensure satisfactory operation of the airborne system, the FAA has provided pilots with the following means of checking VOR receiver accuracy:

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1. VOT or a radiated test signal from an appropriately rated radio repair station. 2. Certified airborne check points. 3. Certified check points on the airport surface. e. A radiated VOT from an appropriately rated radio repair station serves the same purpose as an FAA VOR signal and the check is made in much the same manner as a VOT with the following differences: 1. The frequency normally approved by the Federal Communications Commission is 108.0_MHz. 2. Repair stations are not permitted to radiate the VOR test signal continuously; consequently, the owner or operator must make arrangements with the repair station to have the test signal transmitted. This service is not provided by all radio repair stations. The aircraft owner or operator must determine which AIM 2/14/08 1-1-3 Navigation Aids repair station in the local area provides this service. A representative of the repair station must make an entry into the aircraft logbook or other permanent record certifying to the radial accuracy and the date of transmission. The owner, operator or representa- tive of the repair station may accomplish the necessary checks in the aircraft and make a logbook entry stating the results. It is necessary to verify which test radial is being transmitted and whether you should get a “to” or “from” indication. f. Airborne and ground check points consist of certified radials that should be received at specific points on the airport surface or over specific landmarks while airborne in the immediate vicinity of the airport. 1. Should an error in excess of plus or minus 4_degrees be indicated through use of a ground check, or plus or minus 6 degrees using the airborne check, Instrument Flight Rules (IFR) flight shall not be attempted without first correcting the source of the error. CAUTION- No correction other than the correction card figures supplied by the manufacturer should be applied in making these VOR receiver checks. 2. Locations of airborne check points, ground check points and VOTs are published in the A/FD and are depicted on the A/G voice communications panels on the FAA IFR area chart and IFR enroute low altitude chart. 3. If a dual system VOR (units independent of each other except for the antenna) is installed in the aircraft, one system may be checked against the other. Turn both systems to the same VOR ground facility and note the indicated bearing to that station. The maximum permissible variations between the two indicated bearings is 4 degrees. 1-1-5. Tactical Air Navigation (TACAN) a. For reasons peculiar to military or naval operations (unusual siting conditions, the pitching and rolling of a naval vessel, etc.) the civil VOR/Distance Measuring Equipment (DME) system of air navigation was considered unsuitable for military or naval use. A new navigational system, TACAN, was therefore developed by the military and naval forces to more readily lend itself to military and naval requirements. As a result, the FAA has integrated TACAN facilities with the civil VOR/ DME program. Although the theoretical, or technical principles of operation of TACAN equipment are quite different from those of VOR/DME facilities, the end result, as far as the navigating pilot is concerned, is the same. These integrated facilities are called VORTACs.

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b. TACAN ground equipment consists of either a fixed or mobile transmitting unit. The airborne unit in conjunction with the ground unit reduces the transmitted signal to a visual presentation of both azimuth and distance information. TACAN is a pulse system and operates in the Ultrahigh Frequency (UHF) band of frequencies. Its use requires TACAN airborne equipment and does not operate through conventional VOR equipment. 1-1-6. VHF Omni-directional Range/Tactical Air Navigation (VORTAC) a. A VORTAC is a facility consisting of two components, VOR and TACAN, which provides three individual services: VOR azimuth, TACAN azimuth and TACAN distance (DME) at one site. Although consisting of more than one component, incorporating more than one operating frequency, and using more than one antenna system, a VORTAC is considered to be a unified navigational aid. Both components of a VORTAC are envisioned as operating simultaneously and providing the three services at all times. b. Transmitted signals of VOR and TACAN are each identified by three-letter code transmission and are interlocked so that pilots using VOR azimuth with TACAN distance can be assured that both signals being received are definitely from the same ground station. The frequency channels of the VOR and the TACAN at each VORTAC facility are “paired” in accordance with a national plan to simplify airborne operation. 1-1-7. Distance Measuring Equipment (DME) a. In the operation of DME, paired pulses at a specific spacing are sent out from the aircraft (this is the interrogation) and are received at the ground station. The ground station (transponder) then transmits paired pulses back to the aircraft at the same pulse spacing but on a different frequency. The time required for the round trip of this signal exchange is AIM 2/14/08 1-1-4 Navigation Aids measured in the airborne DME unit and is translated into distance (nautical miles) from the aircraft to the ground station. b. Operating on the line-of-sight principle, DME furnishes distance information with a very high degree of accuracy. Reliable signals may be received at distances up to 199 NM at line-of-sight altitude with an accuracy of better than 1 /2 mile or 3 percent of the distance, whichever is greater. Distance information received from DME equipment is SLANT RANGE distance and not actual horizontal distance. c. Operating frequency range of a DME according to ICAO Annex 10 is from 960 MHz to 1215 MHz. Aircraft equipped with TACAN equipment will receive distance information from a VORTAC automatically, while aircraft equipped with VOR must have a separate DME airborne unit. d. VOR/DME, VORTAC, Instrument Landing System (ILS)/DME, and localizer (LOC)/DME navigation facilities established by the FAA provide course and distance information from collocated components under a frequency pairing plan. Aircraft receiving equipment which provides for automatic DME selection assures reception of azimuth and distance information from a common source when designated VOR/DME, VORTAC, ILS/DME, and LOC/DME are selected.

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e. Due to the limited number of available frequencies, assignment of paired frequencies is required for certain military noncollocated VOR and TACAN facilities which serve the same area but which may be separated by distances up to a few miles. f. VOR/DME, VORTAC, ILS/DME, and LOC/ DME facilities are identified by synchronized identifications which are transmitted on a time share basis. The VOR or localizer portion of the facility is identified by a coded tone modulated at 1020 Hz or a combination of code and voice. The TACAN or DME is identified by a coded tone modulated at 1350_Hz. The DME or TACAN coded identification is transmitted one time for each three or four times that the VOR or localizer coded identification is transmitted. When either the VOR or the DME is inoperative, it is important to recognize which identifier is retained for the operative facility. A single coded identification with a repetition interval of approximately 30 seconds indicates that the DME is operative. g. Aircraft equipment which provides for automatic DME selection assures reception of azimuth and distance information from a common source when designated VOR/DME, VORTAC and ILS/DME navigation facilities are selected. Pilots are cautioned to disregard any distance displays from automatically selected DME equipment when VOR or ILS facilities, which do not have the DME feature installed, are being used for position determination. 1-1-8. Navigational Aid (NAVAID) Service Volumes a. Most air navigation radio aids which provide positive course guidance have a designated standard service volume (SSV). The SSV defines the reception limits of unrestricted NAVAIDs which are usable for random/unpublished route navigation. b. A NAVAID will be classified as restricted if it does not conform to flight inspection signal strength and course quality standards throughout the published SSV. However, the NAVAID should not be considered usable at altitudes below that which could be flown while operating under random route IFR conditions (14_CFR Section 91.177), even though these altitudes may lie within the designated SSV. Service volume restrictions are first published in Notices to Airmen (NOTAMs) and then with the alphabetical listing of the NAVAIDs in the A/FD. c. Standard Service Volume limitations do not apply to published IFR routes or procedures. d. VOR/DME/TACAN Standard Service Volumes (SSV). 1. Standard service volumes (SSVs) are graphi- cally shown in FIG 1-1-1, FIG 1-1-2, FIG 1-1-3, FIG 1-1-4, and FIG 1-1-5. The SSV of a station is indicated by using the class designator as a prefix to the station type designation. EXAMPLE- TVOR, LDME, and HVORTAC. AIM 2/14/08 1-1-5 Navigation Aids FIG 1-1-1 Standard High Altitude Service Volume (See FIG 1-1-5 for altitudes below 1,000 feet). 60,000 ft. 100 NM 130 NM 45,000 ft. 18,000 ft. 14,500 ft. 1,000 ft. 40 NM FIG 1-1-2 Standard Low Altitude Service Volume (See FIG 1-1-5 for altitudes below 1,000 feet). NOTE: All elevations shown are with respect to the station's site elevation (AGL). Coverage is not available in a cone of airspace directly above the facility. 40 NM 18,000 ft. 1,000 ft. FIG 1-1-3 Standard Terminal Service Volume (See FIG 1-1-4 for altitudes below 1,000 feet). 25 NM 12,000 ft. 1,000 ft. AIM 2/14/08 1-1-6 Navigation Aids 2. Within 25 NM, the bottom of the T service volume is defined by the curve in FIG 1-1-4. Within 40 NM, the bottoms of the L and H service volumes are defined by the curve in FIG 1-1-5. (See TBL 1-1-1.)

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e. Nondirectional Radio Beacon (NDB) 1. NDBs are classified according to their intended use. 2. The ranges of NDB service volumes are shown in TBL 1-1-2. The distances (radius) are the same at all altitudes. TBL 1-1-1 VOR/DME/TACAN Standard Service Volumes SSV Class Designator Altitude and Range Boundaries T (Terminal) . . . . . . . . From 1,000 feet above ground level (AGL) up to and including 12,000 feet AGL at radial distances out to 25 NM. L (Low Altitude) . . . . From 1,000 feet AGL up to and including 18,000 feet AGL at radial distances out to 40 NM. H (High Altitude) . . . . From 1,000 feet AGL up to and including 14,500 feet AGL at radial distances out to 40 NM. From 14,500_AGL up to and including 60,000 feet at radial distances out to 100 NM. From 18,000 feet AGL up to and including 45,000 feet AGL at radial distances out to 130 NM. TBL 1-1-2 NDB Service Volumes Class Distance (Radius) Compass Locator 15 NM MH 25 NM H 50 NM* HH 75 NM *Service ranges of individual facilities may be less than 50 nautical miles (NM). Restrictions to service volumes are first published as a Notice to Airmen and then with the alphabetical listing of the NAVAID in the A/FD. FIG 1-1-4 Service Volume Lower Edge Terminal 1000 500 0 0 5 10 15 20 25 DISTANCE TO THE STATION IN NM ALTITUDE IN FEET AIM 2/14/08 1-1-7 Navigation Aids FIG 1-1-5 Service Volume Lower Edge Standard High and Low 1000 500 0 0 10 20 30 40 DISTANCE TO THE STATION IN NM

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ALTITUDE IN FEET 5 15 25 35 1-1-9. Instrument Landing System (ILS) a. General 1. The ILS is designed to provide an approach path for exact alignment and descent of an aircraft on final approach to a runway. 2. The ground equipment consists of two highly directional transmitting systems and, along the approach, three (or fewer) marker beacons. The directional transmitters are known as the localizer and glide slope transmitters. 3. The system may be divided functionally into three parts: (a) Guidance information: localizer, glide slope; (b) Range information: marker beacon, DME; and (c) Visual information: approach lights, touchdown and centerline lights, runway lights. 4. Precision radar, or compass locators located at the Outer Marker (OM) or Middle Marker (MM), may be substituted for marker beacons. DME, when specified in the procedure, may be substituted for the OM. 5. Where a complete ILS system is installed on each end of a runway; (i.e., the approach end of Runway 4 and the approach end of Runway 22) the ILS systems are not in service simultaneously. b. Localizer 1. The localizer transmitter operates on one of 40 ILS channels within the frequency range of 108.10_to 111.95 MHz. Signals provide the pilot with course guidance to the runway centerline. 2. The approach course of the localizer is called the front course and is used with other functional parts, e.g., glide slope, marker beacons, etc. The localizer signal is transmitted at the far end of the runway. It is adjusted for a course width of (full scale fly-left to a full scale fly-right) of 700 feet at the runway threshold. 3. The course line along the extended centerline of a runway, in the opposite direction to the front course is called the back course. CAUTION- Unless the aircraft's ILS equipment includes reverse sensing capability, when flying inbound on the back course it is necessary to steer the aircraft in the direction opposite the needle deflection when making corrections from off-course to on-course. This “flying away from the needle” is also required when flying outbound on the front course of the localizer. Do not use back course signals for approach unless a back course approach procedure is published for that particular runway and the approach is authorized by ATC. AIM 2/14/08 1-1-8 Navigation Aids 4. Identification is in International Morse Code and consists of a three-letter identifier preceded by the letter I ( _ _) transmitted on the localizer frequency. EXAMPLE- I-DIA

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5. The localizer provides course guidance throughout the descent path to the runway threshold from a distance of 18 NM from the antenna between an altitude of 1,000 feet above the highest terrain along the course line and 4,500 feet above the elevation of the antenna site. Proper off-course indications are provided throughout the following angular areas of the operational service volume: (a) To 10 degrees either side of the course along a radius of 18 NM from the antenna; and (b) From 10 to 35 degrees either side of the course along a radius of 10 NM. (See FIG 1-1-6.) FIG 1-1-6 Limits of Localizer Coverage RUNWAY LOCALIZER ANTENNA 10 NM 18 NM LIMITS OF LOCALIZER COVERAGE: THE SAME APPLIES TO A BACK NORMAL AREA COURSE WHEN PROVIDED. 10 10 35 35 6. Unreliable signals may be received outside these areas. c. Localizer Type Directional Aid (LDA) 1. The LDA is of comparable use and accuracy to a localizer but is not part of a complete ILS. The LDA course usually provides a more precise approach course than the similar Simplified Directional Facility (SDF) installation, which may have a course width of 6 or 12 degrees. 2. The LDA is not aligned with the runway. Straight-in minimums may be published where alignment does not exceed 30 degrees between the course and runway. Circling minimums only are published where this alignment exceeds 30 degrees. 3. A very limited number of LDA approaches also incorporate a glideslope. These are annotated in the plan view of the instrument approach chart with a note, “LDA/Glideslope.” These procedures fall under a newly defined category of approaches called Approach with Vertical Guidance (APV) described in paragraph 5-4-5, Instrument Approach Procedure Charts, subparagraph a7(b), Approach with Vertical Guidance (APV). LDA minima for with and without glideslope is provided and annotated on the minima lines of the approach chart as S-LDA/GS and S-LDA. Because the final approach course is not aligned with the runway centerline, additional maneuvering will be required compared to an ILS approach.

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d. Glide Slope/Glide Path 1. The UHF glide slope transmitter, operating on one of the 40 ILS channels within the frequency range 329.15 MHz, to 335.00 MHz radiates its signals in the direction of the localizer front course. The term “glide path” means that portion of the glide slope that intersects the localizer. CAUTION- False glide slope signals may exist in the area of the localizer back course approach which can cause the glide slope flag alarm to disappear and present unreliable glide slope information. Disregard all glide slope signal indications when making a localizer back course approach unless a glide slope is specified on the approach and landing chart. 2. The glide slope transmitter is located between 750 feet and 1,250 feet from the approach end of the runway (down the runway) and offset 250 to 650 feet from the runway centerline. It transmits a glide path beam 1.4 degrees wide (vertically). The signal provides descent information for navigation down to the lowest authorized decision height (DH) specified in the approved ILS approach procedure. The glidepath may not be suitable for navigation below the lowest authorized DH and any reference to glidepath indications below that height must be supplemented by visual reference to the runway environment. Glidepaths with no published DH are usable to runway threshold. 3. The glide path projection angle is normally adjusted to 3 degrees above horizontal so that it intersects the MM at about 200 feet and the OM at AIM 2/14/08 1-1-9 Navigation Aids about 1,400 feet above the runway elevation. The glide slope is normally usable to the distance of 10_NM. However, at some locations, the glide slope has been certified for an extended service volume which exceeds 10 NM. 4. Pilots must be alert when approaching the glidepath interception. False courses and reverse sensing will occur at angles considerably greater than the published path. 5. Make every effort to remain on the indicated glide path. CAUTION- Avoid flying below the glide path to assure obstacle/terrain clearance is maintained. 6. The published glide slope threshold crossing height (TCH) DOES NOT represent the height of the actual glide path on-course indication above the runway threshold. It is used as a reference for planning purposes which represents the height above the runway threshold that an aircraft's glide slope antenna should be, if that aircraft remains on a trajectory formed by the four-mile-to-middle marker glidepath segment.