MSAs

11.12.2007

Submission:

I am not sure whether or not this is a common problem in most countries, but in Norway we have several aerodromes with only an NDB as the primary navigational facility. BASIC GNSS procedures will replace these in the near future, but for now a standard non precision NDB procedure is the only instrument approach procedure available at this aerodrome. My question is if it is allowed to base an MSA on an NDB facility? From a highly conservative point of view there is no distance information available, thus how can a pilot know that he is within 25 NM of the facility? Granted most aircraft will have a GPS or similar available to augment the information sufficiently, but there is no mention of this (at least none that I could find) in DOC 8168.
Second question, quoting our regulations; "A minimum altitude shall apply within a radius of 46 KM (25 NM) of the homing facility on which the instrument approach is based" If the FAF is an NDB, though with a suitable VOR facility located in the immediate vicinity, would it be preferable to publish an MSA based on the VOR?
Morten Bengtson PANS-OPS Avinor

Answer or Commentary:

(I.W
I am not sure about 25nm MSAs that are based solely on an NDB and you are right in thinking that most pilots would use GPS. However after saying that, I have seen MSA sectors on a chart that are based on the ARP with no other navigational aids (other than a LLZ) available.

I think that the best navigational aid should be used. In an ILS approach you would use the VOR/DME for the MSAs. Why not apply the same logic to a NDB approach. I have seen the situation at an airport where the SW and SE sectors are based on an on airport VOR/DME. While on the same chart the NW and NE sectors are based on a VOR/DME situated at an adjacent airport.

I personally think that MSA’s should be GPS based and extend out to 30nm when the receiver switches over to terminal mode.)