Air Traffic Control (ATC) uses the term “no-gyro” to refer to the loss of the primary heading instruments regardless of whether or not the aircraft actually uses gyroscopes to stabilize the primary heading indicator. The phrase “loss of primary flight instrument indicators” can refer to either the mechanical attitude and heading indicator or the integrated information on a primary flight display.
If a pilot losses their primary flight indicators, any radar approach facility, terminal or enroute, can provide no-gyro vectors. But only terminal facilities have the precision needed to provide radar approaches. Terminal facilities can provide a radar approach only if there is an approved radar approach for a particular airport. Any terminal facility can provide no-gyro vectors to a pilot who needs assistance to set up for an electronic instrument approach. However, they do not have the manpower to provide practice no-gyro vectors to all the pilots practicing ‘partial panel’ and the ACS requirement for a non-precision approach with loss of primary flight indicators (Miller, 2009).
There are two types of radar approaches: the Airport Surveillance Radar (ASR) approach and the Precision Approach Radar (PAR) approach. With both radar approaches, a controller provides course guidance and altitude information to the pilot via voice communications. The approaches differ in their accuracy and in the altitude information. The only aircraft equipment required for either approach is an operational communications transceiver. A transponder is not required (Soucy, 2009).
For an ASR approach, the controller issues headings to fly to the pilot in order to intercept and then maintain alignment with the extended centerline of the landing runway. The ASR system provides precise location information, but not precise altitude. In general, the ASR system depends on the Mode C transponder reply for aircraft altitude. The controller can monitor the Mode C altitude, but the Mode C altitude is not part of the approach and the altitude information is advisory only.
On the other hand, the Precision Approach Radar (PAR) is specifically designed as a landing aid that provides aircraft range, azimuth, and elevation information to the controller when the aircraft is on final approach. Similar to the signal transmitted by an instrument landing system (ILS), the PAR system is limited to the extended centerline of the approach runway. Since the radar information used for a PAR approach is considerably more precise than that used for an ASR approach, the accuracy of the approach is greater and lower minimums apply. This article will not cover PAR approaches because they are so rare.