Narrative:

A student pilot and I were on a night cross-country to the grant county airport around midnight. The airport has two tower frequencies; with one of these serving as the CTAF after hours. Although we had looked up this information before the flight and had written the frequency on the navigation log. I used the sectional chart to get the frequency as we approached the airport. Unfortunately; I misread the chart and chose the wrong frequency; although we would not realize this until later. Also; as we approached the airport; and before our flight following was terminated; the controller pointed out a C17 flying toward the airport from the south (we were approaching from the west). We remained west of the airport; did a left 360 to stay out of the way; and announced our position and intentions. As we rolled out of the turn the other aircraft was out of sight. Two runways were lit and we chose the smaller and closer runway 18. Runway 18 is situated on the west edge of the airport and has a right traffic pattern; which would keep us out of the way in case the other aircraft was approaching to land. We announced our position on each leg of the pattern and landed on runway 18 without seeing the other aircraft. We thought the other aircraft may have been passing through and had departed the area (perhaps flying to and from the VOR). After that we made some stop and go landings on the other lit runway 4/22; always announcing our positions on each leg of the pattern. We never did see another aircraft; but on the last circuit in the pattern we did see a ground vehicle on the taxiway near the runway. We received a couple of bursts of static on the radio; which we thought might be that vehicle transmitting. We watched it and it remained stationary. We landed and the vehicle remained stationary. We announced our intentions to takeoff and the vehicle remained stationary. We initiated the takeoff and as the plane was about to liftoff; the vehicle pulled onto the runway and turned toward us; about 1500 ft ahead. I couldn't tell if the vehicle was moving toward us or was stopped; so I wasn't sure if we could stop in time. Since the plane was lifting off; I elected to climb and offset to the right. As we climbed out well above the vehicle; the student looked down and reported that the vehicle appeared to be a pickup and was stopped. We departed the area and again received flight following. We overheard a C17 complaining about a cessna that took off ahead of them; forced them to abort a takeoff; and 'wasn't talking to anybody.' evidently; they were on the larger; unlit runway that intersected the runway we were using. Later on as we tried to figure out what went wrong we discovered my error in selecting the CTAF frequency. I don't know how we missed seeing the other aircraft; perhaps the wing blocked our view; or more likely; we were too fixated on the vehicle. In any case; the whole thing could have been avoided if we had been on the correct frequency.

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Original NASA ASRS Text

Title: Light plane Flight Instructor and Student making late night landings at MWH discover after the fact that they were using the wrong CTAF and had been sharing the airport with a C17.

Narrative: A student pilot and I were on a night cross-country to the Grant County airport around midnight. The airport has two tower frequencies; with one of these serving as the CTAF after hours. Although we had looked up this information before the flight and had written the frequency on the navigation log. I used the sectional chart to get the frequency as we approached the airport. Unfortunately; I misread the chart and chose the wrong frequency; although we would not realize this until later. Also; as we approached the airport; and before our flight following was terminated; the Controller pointed out a C17 flying toward the airport from the south (we were approaching from the west). We remained west of the airport; did a left 360 to stay out of the way; and announced our position and intentions. As we rolled out of the turn the other aircraft was out of sight. Two runways were lit and we chose the smaller and closer Runway 18. Runway 18 is situated on the west edge of the airport and has a right traffic pattern; which would keep us out of the way in case the other aircraft was approaching to land. We announced our position on each leg of the pattern and landed on Runway 18 without seeing the other aircraft. We thought the other aircraft may have been passing through and had departed the area (perhaps flying to and from the VOR). After that we made some stop and go landings on the other lit Runway 4/22; always announcing our positions on each leg of the pattern. We never did see another aircraft; but on the last circuit in the pattern we did see a ground vehicle on the taxiway near the runway. We received a couple of bursts of static on the radio; which we thought might be that vehicle transmitting. We watched it and it remained stationary. We landed and the vehicle remained stationary. We announced our intentions to takeoff and the vehicle remained stationary. We initiated the takeoff and as the plane was about to liftoff; the vehicle pulled onto the runway and turned toward us; about 1500 FT ahead. I couldn't tell if the vehicle was moving toward us or was stopped; so I wasn't sure if we could stop in time. Since the plane was lifting off; I elected to climb and offset to the right. As we climbed out well above the vehicle; the student looked down and reported that the vehicle appeared to be a pickup and was stopped. We departed the area and again received flight following. We overheard a C17 complaining about a Cessna that took off ahead of them; forced them to abort a takeoff; and 'wasn't talking to anybody.' Evidently; they were on the larger; unlit runway that intersected the runway we were using. Later on as we tried to figure out what went wrong we discovered my error in selecting the CTAF frequency. I don't know how we missed seeing the other aircraft; perhaps the wing blocked our view; or more likely; we were too fixated on the vehicle. In any case; the whole thing could have been avoided if we had been on the correct frequency.

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.