ADF Receivers....Gone the way of the dinosuaurs???

[Another KOS]

It is my understanding that:

Part 135 requires 2 independent receivers for navigation. During the enroute phase if the aircraft can be safely navigated over the same route using GPS, and independently using LORAN, VOR, or ADF, the navigation equipment would be considered appropriate to the facilities to be used (i.e. a backup is necessary and due to the potential of common interference, the backup cannot be another GPS).

(Over the North Sea, in areas where there is a lack of navigational coverage from ground based aids, the operator must have procedures in the operations manual to mitigate any failure of the GPS en-route.)

In the US, if an airfield is served by just a GPS approach and the aircraft has a GPS with another type of backup navigation system i.e., VOR, VOR-DME and GPS becomes inoperative, no approach can be started. However if that airfield had GPS and VOR approaches and the GPS went down, either before or during the approach, the VOR could be used for track guidance or for the VOR approach.

If the destination has no ground-based aids, a non-GPS aid would be required for the alternate airport. If a failure of the GPS occurs, the aircraft must execute a missed approach, climb and re-enter the system by navigating to ground-based facility. It is essential that, in the case where the missed approach is due to a failure of the GPS, the go around can be flown safely without track guidance (many US missed approaches and SIDs are based upon heading information and therefore no track information is provided to the pilot).

It is unlikely that any State is opposed to GPS, however, one has only to observe the (subtle) changes of attitude in the US following the publication of a number of important reports (the John Hopkins, the Volpe etc.), to see that this is a complex matter that requires considered policy.

Modern Safety Management Systems has forced hazard analyses to be conducted for any new equipment/principle/method/procedure. This was not the case when DECCA was adopted as the navigation aid of preference in the North Sea.

GLS: it is not JARs that prescribe the standards of equipment it is TSOs - which in this case is a common text used by most States.

My contention is that the best solution to these problems will come with the co-location of GPS and INS in a single and inexpensive box (my understanding is that the BA609 is today flying with such a system installed).

It is also my undertanding that:

Any proposed amendment to CAA regulations on descent below the MSA, is probably based on the need to remove the anomaly of the wording that permits the descent when on an 'approach to landing' (my words not theirs but you will see the point). The present wording does not require this to be 'on a published procedure' - with the obvious potential for 'home grown' procedures. (There was also a recent amendment to JARs to permit a descent below MSA in accordance with procedures accepted by the authority - this was to provide a facility for an en-route descent over the sea using the Radar to provide obstacle clearance.)

There was representation to the CAA during the discussions on this change to ensure that, when closing this loophole, operators' 'discrete procedures' (contained in the operations manual, or the Jeppersen or the AERAD) would still be permitted - including generic ARA procedures.