Narrative:

Stage check for instrument training, flight on and off victor airways with diversion to alternate airport. Flight departed sat airport towards thx VOR. Climbed to 7500 ft MSL to get above a broken cloud deck, and winds from south at approximately 35 KTS. About 9 NM north of thx VOR, gave student a situation where WX had deteriorated and could not return to sat. Hyi airport was selected as divert airfield. Student made diversion under simulated instrument conditions (hood). Student estimated route using radials off thx and sat vors and computed an ETA to hyi. I used onboard GPS to check heading and ETA to alternate. The student's calculations appeared to be good estimates, so I turned off the GPS and followed flight path using VFR sectional. Landmarks were visible through broken cloud layer and flight progressed satisfactory along diversion route. Just past sequin, tx, I stopped using the VFR sectional, thinking hyi would be within sight after descending below the broken cloud deck. At ETA, I had the student take off hood and start looking for the divert airfield. Descended through a break in the cloud layer -- tops were 6500 ft MSL and bases 4500 ft MSL. Once below the cloud layer, visibility decreased 5-8 SM in haze. I was expecting to see hyi after descending below the cloud layer. Visibility to the west was worse due to setting sun and haze. I saw what appeared to be hyi and told the student to continue on present course. After 3 mins, student saw an airfield and started to descend. It took me a moment to recognize the airfield layout was not hyi and was actually aus. I turned on the GPS to get a bearing and distance from aus. By the time it provided an operational readout, it indicated we were 8.5 NM from the field. We had now descended to 3800 ft MSL. I had the student start a 180 degree turn and told him to climb back to 4000 ft MSL. I recognized several landmarks and interstate 35 off our right side. I told the student to stay on a heading of 210 degrees and descend to 3500 ft MSL. I entered hyi into the GPS and it indicated the airfield was 10 NM away. Entered the pattern and landed. Called aus approach and asked if they were tracking an aircraft had inadvertently entered their class C airspace. They said yes. And I explained it was our aircraft. The controller said 'you realize you entered class C without authority/authorized.' I said I understood. I then asked if I needed to take any action with them. They indicated no, since there was no traffic conflict involved. Problem arose when I did not see hyi (divert airfield) after reaching ETA point and starting a descent from 7500 ft MSL with the visibility blocked by a cloud layer, then obscured by haze. Contributing factors: not keeping track of visual landmarks after sequin, tx. Not updating ETA with strong and gusting winds which affected our ground speed. Expecting divert airfield to be visible after descent. Setting sun and haze precluded from looking west where divert airfield was actually located along route of flight. Lessons learned: maintain position awareness even if familiar with route landmarks. Don't have expectations of in-flight estimates to be accurate. Verify/update flight calculations. Monitor ATC facilities when operating in proximity to class C airspace. Be more vigilant when visibility is worse than expected. Be candid with mistakes. Student appreciated my contacting ATC to explain what had happened.

Related reports:

Google
 

Original NASA ASRS Text

Title: COMPANY INSTRUCTOR PLT AND STUDENT MISIDENT ALTERNATE ARPT AND PENETRATE AUS CLASS C AIRSPACE BEFORE RECOGNIZING ERROR.

Narrative: STAGE CHK FOR INST TRAINING, FLT ON AND OFF VICTOR AIRWAYS WITH DIVERSION TO ALTERNATE ARPT. FLT DEPARTED SAT ARPT TOWARDS THX VOR. CLBED TO 7500 FT MSL TO GET ABOVE A BROKEN CLOUD DECK, AND WINDS FROM S AT APPROX 35 KTS. ABOUT 9 NM N OF THX VOR, GAVE STUDENT A SIT WHERE WX HAD DETERIORATED AND COULD NOT RETURN TO SAT. HYI ARPT WAS SELECTED AS DIVERT AIRFIELD. STUDENT MADE DIVERSION UNDER SIMULATED INST CONDITIONS (HOOD). STUDENT ESTIMATED RTE USING RADIALS OFF THX AND SAT VORS AND COMPUTED AN ETA TO HYI. I USED ONBOARD GPS TO CHK HDG AND ETA TO ALTERNATE. THE STUDENT'S CALCULATIONS APPEARED TO BE GOOD ESTIMATES, SO I TURNED OFF THE GPS AND FOLLOWED FLT PATH USING VFR SECTIONAL. LANDMARKS WERE VISIBLE THROUGH BROKEN CLOUD LAYER AND FLT PROGRESSED SATISFACTORY ALONG DIVERSION RTE. JUST PAST SEQUIN, TX, I STOPPED USING THE VFR SECTIONAL, THINKING HYI WOULD BE WITHIN SIGHT AFTER DSNDING BELOW THE BROKEN CLOUD DECK. AT ETA, I HAD THE STUDENT TAKE OFF HOOD AND START LOOKING FOR THE DIVERT AIRFIELD. DSNDED THROUGH A BREAK IN THE CLOUD LAYER -- TOPS WERE 6500 FT MSL AND BASES 4500 FT MSL. ONCE BELOW THE CLOUD LAYER, VISIBILITY DECREASED 5-8 SM IN HAZE. I WAS EXPECTING TO SEE HYI AFTER DSNDING BELOW THE CLOUD LAYER. VISIBILITY TO THE W WAS WORSE DUE TO SETTING SUN AND HAZE. I SAW WHAT APPEARED TO BE HYI AND TOLD THE STUDENT TO CONTINUE ON PRESENT COURSE. AFTER 3 MINS, STUDENT SAW AN AIRFIELD AND STARTED TO DSND. IT TOOK ME A MOMENT TO RECOGNIZE THE AIRFIELD LAYOUT WAS NOT HYI AND WAS ACTUALLY AUS. I TURNED ON THE GPS TO GET A BEARING AND DISTANCE FROM AUS. BY THE TIME IT PROVIDED AN OPERATIONAL READOUT, IT INDICATED WE WERE 8.5 NM FROM THE FIELD. WE HAD NOW DSNDED TO 3800 FT MSL. I HAD THE STUDENT START A 180 DEG TURN AND TOLD HIM TO CLB BACK TO 4000 FT MSL. I RECOGNIZED SEVERAL LANDMARKS AND INTERSTATE 35 OFF OUR R SIDE. I TOLD THE STUDENT TO STAY ON A HDG OF 210 DEGS AND DSND TO 3500 FT MSL. I ENTERED HYI INTO THE GPS AND IT INDICATED THE AIRFIELD WAS 10 NM AWAY. ENTERED THE PATTERN AND LANDED. CALLED AUS APCH AND ASKED IF THEY WERE TRACKING AN ACFT HAD INADVERTENTLY ENTERED THEIR CLASS C AIRSPACE. THEY SAID YES. AND I EXPLAINED IT WAS OUR ACFT. THE CTLR SAID 'YOU REALIZE YOU ENTERED CLASS C WITHOUT AUTH.' I SAID I UNDERSTOOD. I THEN ASKED IF I NEEDED TO TAKE ANY ACTION WITH THEM. THEY INDICATED NO, SINCE THERE WAS NO TFC CONFLICT INVOLVED. PROB AROSE WHEN I DID NOT SEE HYI (DIVERT AIRFIELD) AFTER REACHING ETA POINT AND STARTING A DSCNT FROM 7500 FT MSL WITH THE VISIBILITY BLOCKED BY A CLOUD LAYER, THEN OBSCURED BY HAZE. CONTRIBUTING FACTORS: NOT KEEPING TRACK OF VISUAL LANDMARKS AFTER SEQUIN, TX. NOT UPDATING ETA WITH STRONG AND GUSTING WINDS WHICH AFFECTED OUR GND SPD. EXPECTING DIVERT AIRFIELD TO BE VISIBLE AFTER DSCNT. SETTING SUN AND HAZE PRECLUDED FROM LOOKING W WHERE DIVERT AIRFIELD WAS ACTUALLY LOCATED ALONG RTE OF FLT. LESSONS LEARNED: MAINTAIN POS AWARENESS EVEN IF FAMILIAR WITH RTE LANDMARKS. DON'T HAVE EXPECTATIONS OF INFLT ESTIMATES TO BE ACCURATE. VERIFY/UPDATE FLT CALCULATIONS. MONITOR ATC FACILITIES WHEN OPERATING IN PROX TO CLASS C AIRSPACE. BE MORE VIGILANT WHEN VISIBILITY IS WORSE THAN EXPECTED. BE CANDID WITH MISTAKES. STUDENT APPRECIATED MY CONTACTING ATC TO EXPLAIN WHAT HAD HAPPENED.

Data retrieved from NASA's ASRS site as of July 2007 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.