Bil local controller described low altitude alert event when aircraft's descent on the VOR/DME runwa...

Narrative:

I took local control and was briefed that aircraft X was approved for opposite direction practice approach (IMC). The relieved controller suggested I 'keep an eye on him;' although he was not more specific. Weather at the time was IFR; ceilings approximately 700 AGL; with 1 SM visibility and light snow. Aircraft X checked on my frequency inbound. He was told to continue; vehicles on the runway. There was no readback. After he checked on; I noticed his altitude did not look right; so I referenced the approach plate and crosschecked his altitude at the FAF; the MSAW alert went off. Crossing altitude at the FAF was 5200'; the aircraft was at approximately 4500'. There was discussion among the controllers in the cab as to which altitude to give him; with the MDA suggested; although he was still outside the FAF. I thought it did not make much sense to give him the MDA; since that would descend him further (4040' MSL); but decided I had to give him something and told him to check altitude immediately and recommended he execute a missed approach. There was no readback. I tried to contact him again; using only his call sign and no message; and he did respond. When I issued the alert again with the climb recommendation; he read back 'climbing out.' he did appear to start a climb; up to 4600'; and then seemed to level off; so I inquired whether he was still on the approach. He replied that he was receiving a lot of static in the transmission; which is a known issue to the east of the airport. I instructed the snow removal vehicles to exit the runway at this point; not certain what his intentions were; and repeated my inquiry. He stated again that he had a lot of static and he wasn't catching my transmissions; then reported on the missed climbing through 4600'. I instructed him to proceed direct the VORTAC; which had been communicated via ARTS scratchpad to be his missed approach instruction. Three minutes later; after he was west of the airport and I could confirm his climbout; I transferred him back to departure. Recommendation; this was the first safety/terrain alert I had issued. I knew the phraseology from classroom and training; but had never had to use it and was stuck as to which altitude to give the pilot given his position on the approach. As a result; the phraseology came out incorrectly and did not sound as forceful as it should have. I had to issue another low altitude alert later in the evening; which sounded much more confident; and the pilot (different aircraft) responded appropriately. Additionally; although we cannot refuse a pilot a legal request; it was not advisable for this particular GA pilot being out practicing IFR approaches in actual IFR weather. I have not seen this aircraft practicing instrument approaches in VFR conditions; and it showed in his inability to hold altitude on the VOR DME runway 28R approach; as well as his inability to track radials and perform published VOR holding patterns in subsequent approaches. He was practicing non-precision approaches for which the weather was barely at minimums or below minimums. In this situation; it was intimidating to be the controller who might have to talk him down in an emergency; seeing as he wouldn't legally be able to land on the approaches he was attempting.

Original NASA ASRS Text

Title: BIL Local Controller described low altitude alert event when aircraft's descent on the VOR/DME Runway 28 approach activated the alarm; pilot acknowledging that the GPS was programed incorrectly prompting the early descent.

Narrative: I took Local Control and was briefed that Aircraft X was approved for opposite direction practice approach (IMC). The relieved controller suggested I 'keep an eye on him;' although he was not more specific. Weather at the time was IFR; ceilings approximately 700 AGL; with 1 SM visibility and light snow. Aircraft X checked on my frequency inbound. He was told to continue; vehicles on the runway. There was no readback. After he checked on; I noticed his altitude did not look right; so I referenced the approach plate and crosschecked his altitude at the FAF; the MSAW alert went off. Crossing altitude at the FAF was 5200'; the aircraft was at approximately 4500'. There was discussion among the controllers in the cab as to which altitude to give him; with the MDA suggested; although he was still outside the FAF. I thought it did not make much sense to give him the MDA; since that would descend him further (4040' MSL); but decided I had to give him something and told him to check altitude immediately and recommended he execute a missed approach. There was no readback. I tried to contact him again; using only his call sign and no message; and he did respond. When I issued the alert again with the climb recommendation; he read back 'climbing out.' He did appear to start a climb; up to 4600'; and then seemed to level off; so I inquired whether he was still on the approach. He replied that he was receiving a lot of static in the transmission; which is a known issue to the east of the airport. I instructed the snow removal vehicles to exit the runway at this point; not certain what his intentions were; and repeated my inquiry. He stated again that he had a lot of static and he wasn't catching my transmissions; then reported on the missed climbing through 4600'. I instructed him to proceed direct the VORTAC; which had been communicated via ARTS scratchpad to be his missed approach instruction. Three minutes later; after he was west of the airport and I could confirm his climbout; I transferred him back to departure. Recommendation; this was the first safety/terrain alert I had issued. I knew the phraseology from classroom and training; but had never had to use it and was stuck as to which altitude to give the pilot given his position on the approach. As a result; the phraseology came out incorrectly and did not sound as forceful as it should have. I had to issue another low altitude alert later in the evening; which sounded much more confident; and the pilot (different aircraft) responded appropriately. Additionally; although we cannot refuse a pilot a legal request; it was not advisable for this particular GA pilot being out practicing IFR approaches in actual IFR weather. I have not seen this aircraft practicing instrument approaches in VFR conditions; and it showed in his inability to hold altitude on the VOR DME Runway 28R approach; as well as his inability to track radials and perform published VOR holding patterns in subsequent approaches. He was practicing non-precision approaches for which the weather was barely at minimums or below minimums. In this situation; it was intimidating to be the controller who might have to talk him down in an emergency; seeing as he wouldn't legally be able to land on the approaches he was attempting.

Data retrieved from NASA's ASRS site as of April 2012 and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.

Attributes
ACN	867648
Time
Date	201001
Local Time Of Day	0001-0600
Place
Locale Reference	BIL.TRACON
State Reference	MT
Aircraft 1
Make Model Name	Cessna Super Skywagon/Super Skylane
Operating Under FAR Part	Part 91
Flight Phase	Final Approach
Route In Use	Other Instrument Approach
Flight Plan	IFR
Person 1
Function	Local
Person 2
Function	Captain Instructor Pilot Not Flying
Experience	Flight Crew Last 90 Days 50 Flight Crew Total 17900 Flight Crew Type 300
Events
Anomaly	Inflight Event / Encounter CFTT / CFIT

Bil local controller described low altitude alert event when aircraft's descent on the VOR/DME runway 28 approach activated the alarm; pilot acknowledging that the GPS was programed incorrectly prompting the early descent.