Narrative:

I initiated a night VFR flight from the spokane area to pullman/moscow regional airport (puw). The purpose of the flight was to provide night instruction to a friend of mine seeking to meet the experience requirements for a private pilot certificate; the flight was intended to meet the night cross country requirement. We received a standard VFR weather briefing from FSS in which the current conditions at our departure airport were reported as 2200 scattered and 6000 overcast; with pullman reporting 6000 overcast. Spokane international airport (geg); was reporting 1900 scattered at the time of our departure. Along our direct course line to pullman there is higher terrain called tower mountain up to 4600 feet MSL; and usually a departure to the south is conducted to the east of this terrain feature; through a route called micah gap; or to the west in which; in the absence of contact with spokane approach control; must remain below 4200 feet to remain clear of the spokane international class C airspace. Due to some lingering clouds in the vicinity of micah gap; I elected to fly the west route and to maintain outside the class C by monitoring our position on the moving map feature of a handheld garmin GPS. As we proceeded 8 miles south of our departure airport; we discovered we were flying below a cloud layer about 1000 feet above our flight altitude of 3300 feet. At the time this allowed us to easily maintain required 1000 feet altitude above the southern residential area; and to also have required clearance below the clouds. I discussed with my friend that we could maintain our current altitude for about 10 more miles; but that further down our route the terrain would start to steadily rise; so we knew we could not continue that course at that altitude. At the time we were still not concerned because the layer above us was very thin and we could see stars above us at times. Also; we anticipated the layer would not extend very far south of spokane. A few minutes later; we found ourselves still under this layer; which now appeared thicker; and we became concerned that we could no longer stay 1000 feet AGL while remaining 500 feet below cloud bases. I decided we should turn to the west; where I anticipated the layer would no longer exist. I will also note here that in the night conditions we were flying in it was difficult to see the cloud layer and determine how high above us it was. We flew west; while trying to follow our position on the GPS moving map to ensure continued clearance from the class C airspace. As we proceeded west the situation with the cloud layer and ground clearance did not improve to my satisfaction; so I decided to have my friend turn around and return the way we had come. A minute or two after turning back to the east; I observed a large section of clear sky just north of us that provided sufficient space to maneuver and climb above the layer. I took control of the airplane and initiated a circling climb; while asking my friend to monitor our position on the moving map to make sure we were not near the spokane class C. At this point there was some confusion on reading the GPS; and either the GPS signal was compromised or the display page was changed inadvertently to a page that did not depict the airspace. I will also note I was seated in the back of this tandem-seat aircraft and the GPS was mounted in the front seat; so I could not manipulate or make inputs to the GPS; and could not clearly read the display at all times. For the next several minutes; my attention was mostly dedicated to controlling the airplane in the climbing turn and maintaining safe VFR distances from the clouds. Without trouble we were able to get above the layer at an altitude to 3800 feet MSL. I again wanted to check our position relative to the airspace; and I was able to see at this time that we were roughly 3 miles south of the outer ring of the airspace; on a southerly (away from the airspace) heading. At that point my friendinformed me he thought he had observed us closer to the edge of the C class airspace at the time we leveled off at 3800 feet. Due to this short period in which the GPS did not have full reception or was not configured to display properly; I became unsure whether I had maintained clearance from the airspace during the full duration of our circling/climbing maneuver. At that point I studied the sectional chart more carefully to try to determine my position to both a.) relative to the outer ring of the airspace and b.) my position relative where the floor of the outer ring changes from 4200 to 3700 feet. Again; I concluded I could not say with complete certainty that I had remained outside the class C at all times. I contemplated this as we then continued to pullman airport in excellent VFR conditions to an uneventful landing. On later analysis; there are a number of factors that I identified; as well as a less-than-optimal decision process that contributed to this position uncertainty event. In retrospect; I believe it may have been unwise to not plan to use radar service/flight following; which would have obviated the entire problem of needing to remain clear of the class C airspace. The airplane that we used has a very weak communication radio; with both communication and transponder antennas mounted on the belly near the landing gear. In the past; I have often had trouble when trying to use flight following both with hearing approach control and with approach controllers being able to maintain a consistent secondary target any time below 4000 feet. So this led to the decision to try to stay out of the airspace. So not only should I have been more wise to use radar service; but perhaps also it would have been better to use a different airplane; one that is more capable and better equipped. I came away from this experience realizing that using an airplane with basic VFR equipment on a night flight in which there was any question of having weather issues was also; perhaps; not the best choice. The spokane class C is designed in such a way as to give added room for airplanes to depart from and arrive to spokane from the south; with the floor of the outer ring being raised where the terrain is higher. This is effective; but depending on equipment; radio power and antenna geometry; aircraft at low altitudes in this south region often experience difficulties maintaining good radio and radar contact with the spokane TRACON. I believe there are already some measures being taken that will improve this situation such as implementation of ads-B systems in the coming years. Handheld GPS units are very useful and have increased safety in many ways; but it should be recognized the limitations of such portable systems and that they are susceptible to having inconsistent reception; especially if the antennas are not situated in an optimal manner. It is good that pilots be reminded of where handheld units are most effectively utilized; which I would limit to situations of good VFR and redundant means of position verification. I want to use this experience to discuss with other pilots the added complexities of night flying and the additional planning that should be taken in such situations to make sure all safety considerations are met to the fullest degree.

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Original NASA ASRS Text

Title: PA18 Instructor describes a night cross country flight with a student during which weather and a hand held GPS unit conspire to produce a Class C airspace incursion.

Narrative: I initiated a night VFR flight from the Spokane area to Pullman/Moscow Regional airport (PUW). The purpose of the flight was to provide night instruction to a friend of mine seeking to meet the experience requirements for a private pilot certificate; the flight was intended to meet the night cross country requirement. We received a standard VFR weather briefing from FSS in which the current conditions at our departure airport were reported as 2200 scattered and 6000 overcast; with Pullman reporting 6000 overcast. Spokane International airport (GEG); was reporting 1900 scattered at the time of our departure. Along our direct course line to Pullman there is higher terrain called tower mountain up to 4600 feet MSL; and usually a departure to the south is conducted to the east of this terrain feature; through a route called Micah gap; or to the west in which; in the absence of contact with Spokane approach control; must remain below 4200 feet to remain clear of the Spokane international Class C airspace. Due to some lingering clouds in the vicinity of Micah gap; I elected to fly the west route and to maintain outside the class C by monitoring our position on the moving map feature of a handheld Garmin GPS. As we proceeded 8 miles south of our departure airport; we discovered we were flying below a cloud layer about 1000 feet above our flight altitude of 3300 feet. At the time this allowed us to easily maintain required 1000 feet altitude above the southern residential area; and to also have required clearance below the clouds. I discussed with my friend that we could maintain our current altitude for about 10 more miles; but that further down our route the terrain would start to steadily rise; so we knew we could not continue that course at that altitude. At the time we were still not concerned because the layer above us was very thin and we could see stars above us at times. Also; we anticipated the layer would not extend very far south of Spokane. A few minutes later; we found ourselves still under this layer; which now appeared thicker; and we became concerned that we could no longer stay 1000 feet AGL while remaining 500 feet below cloud bases. I decided we should turn to the west; where I anticipated the layer would no longer exist. I will also note here that in the night conditions we were flying in it was difficult to see the cloud layer and determine how high above us it was. We flew west; while trying to follow our position on the GPS moving map to ensure continued clearance from the Class C airspace. As we proceeded west the situation with the cloud layer and ground clearance did not improve to my satisfaction; so I decided to have my friend turn around and return the way we had come. A minute or two after turning back to the east; I observed a large section of clear sky just north of us that provided sufficient space to maneuver and climb above the layer. I took control of the airplane and initiated a circling climb; while asking my friend to monitor our position on the moving map to make sure we were not near the Spokane class C. At this point there was some confusion on reading the GPS; and either the GPS signal was compromised or the display page was changed inadvertently to a page that did not depict the airspace. I will also note I was seated in the back of this tandem-seat aircraft and the GPS was mounted in the front seat; so I could not manipulate or make inputs to the GPS; and could not clearly read the display at all times. For the next several minutes; my attention was mostly dedicated to controlling the airplane in the climbing turn and maintaining safe VFR distances from the clouds. Without trouble we were able to get above the layer at an altitude to 3800 feet MSL. I again wanted to check our position relative to the airspace; and I was able to see at this time that we were roughly 3 miles south of the outer ring of the airspace; on a southerly (away from the airspace) heading. At that point my friendinformed me he thought he had observed us closer to the edge of the C class airspace at the time we leveled off at 3800 feet. Due to this short period in which the GPS did not have full reception or was not configured to display properly; I became unsure whether I had maintained clearance from the airspace during the full duration of our circling/climbing maneuver. At that point I studied the sectional chart more carefully to try to determine my position to both a.) relative to the outer ring of the airspace and b.) my position relative where the floor of the outer ring changes from 4200 to 3700 feet. Again; I concluded I could not say with complete certainty that I had remained outside the class C at all times. I contemplated this as we then continued to Pullman airport in excellent VFR conditions to an uneventful landing. On later analysis; there are a number of factors that I identified; as well as a less-than-optimal decision process that contributed to this position uncertainty event. In retrospect; I believe it may have been unwise to not plan to use radar service/flight following; which would have obviated the entire problem of needing to remain clear of the Class C airspace. The airplane that we used has a very weak communication radio; with both communication and transponder antennas mounted on the belly near the landing gear. In the past; I have often had trouble when trying to use flight following both with hearing approach control and with approach controllers being able to maintain a consistent secondary target any time below 4000 feet. So this led to the decision to try to stay out of the airspace. So not only should I have been more wise to use radar service; but perhaps also it would have been better to use a different airplane; one that is more capable and better equipped. I came away from this experience realizing that using an airplane with basic VFR equipment on a night flight in which there was any question of having weather issues was also; perhaps; not the best choice. The Spokane Class C is designed in such a way as to give added room for airplanes to depart from and arrive to Spokane from the south; with the floor of the outer ring being raised where the terrain is higher. This is effective; but depending on equipment; radio power and antenna geometry; aircraft at low altitudes in this south region often experience difficulties maintaining good radio and radar contact with the Spokane TRACON. I believe there are already some measures being taken that will improve this situation such as implementation of ADS-B systems in the coming years. Handheld GPS units are very useful and have increased safety in many ways; but it should be recognized the limitations of such portable systems and that they are susceptible to having inconsistent reception; especially if the antennas are not situated in an optimal manner. It is good that pilots be reminded of where handheld units are most effectively utilized; which I would limit to situations of good VFR and redundant means of position verification. I want to use this experience to discuss with other pilots the added complexities of night flying and the additional planning that should be taken in such situations to make sure all safety considerations are met to the fullest degree.

Data retrieved from NASA's ASRS site 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.