GPS Procedures -Cont.

T-34C INSTRUMENTS

CHAPTER SEVEN

There is important information to know when using the GPS for IFR navigation and instrument

approaches. As a part of the system integrity, the GPS receiver monitors and predicts satellite

orbital position and geometry. The process of monitoring and predicting satellite position is

known as Receiver Autonomous Integrity Monitoring (RAIM). RAIM verifies the predicted

orbital position of the satellite or satellites used for a particular approach matches the actual

orbital position(s). If the positions do not match, the accuracy of the GPS position data may not

meet non-precision approach requirements. In this case, the GPS receiver will generate a message

notifying the pilot that GPS data should not be used for the approach. RAIM outages may occur

due to an insufficient number of satellites, unsuitable satellite position, terrain masking, aircraft

dynamics (changes in pitch or bank angle) or improper barometric altitude data input.

Prior to any IFR GPS operation, the pilot must check for planned GPS outages at the departure

and destination airports by either calling an FSS preflight briefer or checking online NOTAM

information using "KGPS" as the airfield identifier. The military provides airfield specific GPS

RAIM (M-series) NOTAM's for non-precision approach procedures at military airfields. During

longer flights, predictive RAIM at the destination should be checked manually by using the Status

5 (STA5) page of the KLN 900. This may provide early indications that an unscheduled satellite

outage has occurred since takeoff. Predictive RAIM cannot account for terrain masking problems

associated with flights in the vicinity of mountainous terrain, for unplanned satellite outages or for

internal equipment malfunctions. Since the relative positions of the satellites are constantly

changing, prior experience with the airport does not guarantee reception at all times, and RAIM

availability should always be checked.

NOTE

For the purposed of alternate field selection a compatible and

operational non-GPS approach SHALL exist at the alternate airport.

The Super NAV 5 page has been specifically designed to provide most of the functions needed

for non-precision approaches. This page provides an interface that presents pertinent navigation

information, a way to access the flight plan, and a graphic presentation of the present position

relative to the flight plan waypoints. You will find this page to be very useful in conducting non-

precision approaches. It can be accessed by selected the NAV 5 page on both the left and right

side of the GPS console.

When conducting GPS approaches it is important to understand the differences between the OBS

and LEG modes of operation of the KLN900. The OBS mode provides no automatic sequencing

between waypoints. OBS mode only provides navigation to the active waypoint by way of the

course dialed into the OBS knob below the CDI. When the GPS is in OBS mode, rotating the

OBS knob will rotate the course select line, but will not change course select line when in LEG

mode. LEG mode provides Automatic Waypoint Sequencing, navigation to the active waypoint

via a direct routing from your present position and Turn Anticipation. When using Turn

Anticipation, the waypoint (WPT) light will begin to flash 20 seconds prior to turn. When the

light goes steady, begin the turn to the new course. This will be used when flying approaches or

any time the WPT is a Fly-Over WPT. OBS mode is used when holding, conducting a procedure

turn outbound or when intercepting a final approach course via radar vectors. LEG mode is used

INSTRUMENT NAVIGATION 7-27