| Facility: |
| GS |
| Summary: |
| This document emphasizes the importance of a facility shutdown and the related coordination procedures when performing Glilde Slope (GS) system phasing. During this periodic maintenance procedure, there is a portion of time when the radiated signal will indicate to a pilot that the GS is operational and, worse yet, give the pilot a false indication that the aircraft is on the correct glide angle, regardless of the position of the aircraft. |
| Alert: |
| Recently, the FAA has been advised of instances wherein pilots reported the GS useable although the system had been NOTAM'd 'out of service'. This alert is a reminder to ILS specialists that during phasing procedures, when the facility is radiating in quadrature, the radiated signal will look like an 'on-path' signal to the pilot regardless of the position of the aircraft, i.e., above or below the glide path. ATC should also be aware of this and notify all aircraft in the approach landing airspace of this fact.
In accordance with the ILS Handbook, Order 6750.49A, a facility shutdown is required whenever performing system phasing. It is the responsibility of the specialist to ensure a facility shutdown has been requested, coordinated and approved through the appropriate channels. Furthermore, it is good maintenance practice to ensure Air Traffic Control is fully aware of the shutdown and the Notice to Airmen (NOTAM) has been issued before performing maintenance.
Procedures are being investigated in an effort to reduce the number of possible coordination link failures. The FAA has assembled a small team to evaluate our coordination system for single points of failure and to improve the content of maintenance handbook warnings. Until such time further guidance is distributed, abide by any and all standard operating procedures when coordinating shutdowns.
If you have any questions or concerns, please contact Mickey Lindecker, AOS-241, at (405) 954-5197. |
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