Narrative:

While conducting a primary dual instructional flight under VFR as a CFI, I flew into an area of IMC while landing at a tower-controled airport. The ATIS at boeing field indicated 5 mi visibility with a ceiling of at least 2000 ft. However, from 6 mi to the south as I radioed the tower prior to entering class D airspace, the field was not yet visible. The field is located in a valley and was obscured by what appeared to be mist. Flight visibility in all directions around me was approximately 5 mi, but visibility north towards the field appeared to be around 3 mi. I was told by the tower to make a straight-in approach to runway 31R. I also heard a boeing jet on the ILS back course approach being cleared to land on runway 31L. I did not know how far behind me the jet was when it was cleared to land. Closer to the airport, I called for and received clearance to land on runway 31R. As I proceeded towards the runway, which I still could not see, visibility deteriorated to about 2 mi in blowing snow. I was already at pattern altitude (1000 ft). I followed a highway (I-5) that I knew from experience would lead me directly to the runway. It did, and I was easily able to intercept the VASI at pattern altitude and land without incident. I tuned in the ATIS while taxiing. A 'special observation' indicated that the field was IFR with visibility of 2 mi in snow. The time given for the 'special observation' was several mins before I had landed. Apparently a fast- moving, localized, unforecast snow squall (in seattle?!) had moved in from lake washington and obscured only boeing field. Nearby renton and sea-tac remained VFR. Analysis: my decision to continue VFR in class D airspace towards a runway I could not see was clearly an error. When I requested and was granted clearance to land from 3 mi away, I still could not see the runway. I knew I was making a decision, and I knew that it was probably the wrong one. However, somewhat incredibly, in the heat of the moment, I did not immediately think of what the right decision might be, so I blundered forward. What I should have done: on my initial call-up from 6 mi away, I should have indicated to the tower that the field did not appear to be VFR, and to please advise. At that time, I could easily have requested a special VFR. Certainly upon requesting my landing clearance, I should have told the tower that the field did not appear to be VFR. By that point, already in class D, I could not have obtained a special VFR clearance, but some sort of arrangements could have been made. In any event, I should have executed a 180 degree turn upon entering IMC, since I knew that VFR conditions existed behind me, and I did not know how bad the visibility was in front of me. In conditions of blowing snow, it could easily have deteriorated to 1 mi or less. In general, more communication earlier on with the tower would have prevented me from getting into this situation. Reasons I did not make the proper decisions: there was no push-to-talk button on the r-hand yoke, forcing me to use the hand-held microphone. The microphone had fallen to the floor in front of me, and, as visibility deteriorated, I was concentrating on my flying and hesitated to reach down and pick it up. Moreover, the tower had told me that they had difficulty hearing my xmissions from the microphone (and from the crummy aircraft radios). I hesitated to execute a 180 degree turn out of IMC because I did not know the position of the boeing jet behind me. It might have been right on my tail, and a blind 180 degree turn towards it could have been disastrous. My student had told me that she needed to be on the ground by XA00 pm, and time was running short. As a fairly new CFI with a fairly new student, I did not want to appear that I was unsure of what to do. (However, in previous sits, this had never been a problem for me.) after this flight, my student left quickly to get to an appointment. Before our lesson the next day, however, I gave her a lengthy and candid evaluation of the errors in judgement I had made, and we had a very productive discussion of human factors and aviation decision-making in general.

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Original NASA ASRS Text

Title: INSTRUCTOR PLT OF A C172 OF A DUAL TRAINING FLEW INTO IMC WX CONDITIONS DURING RETURN TO HOME BASE. THE FLT VISIBILITY WAS REDUCED BY A SNOW SHOWER WHICH TOOK THE RPTR BY SURPRISE. HE DID NOT DO A 180 DEG TURN BACK TO VFR WX SINCE THERE WAS A RPTED B727 BEHIND HIM MAKING AN APCH TO THE ADJACENT PARALLEL RWY.

Narrative: WHILE CONDUCTING A PRIMARY DUAL INSTRUCTIONAL FLT UNDER VFR AS A CFI, I FLEW INTO AN AREA OF IMC WHILE LNDG AT A TWR-CTLED ARPT. THE ATIS AT BOEING FIELD INDICATED 5 MI VISIBILITY WITH A CEILING OF AT LEAST 2000 FT. HOWEVER, FROM 6 MI TO THE S AS I RADIOED THE TWR PRIOR TO ENTERING CLASS D AIRSPACE, THE FIELD WAS NOT YET VISIBLE. THE FIELD IS LOCATED IN A VALLEY AND WAS OBSCURED BY WHAT APPEARED TO BE MIST. FLT VISIBILITY IN ALL DIRECTIONS AROUND ME WAS APPROX 5 MI, BUT VISIBILITY N TOWARDS THE FIELD APPEARED TO BE AROUND 3 MI. I WAS TOLD BY THE TWR TO MAKE A STRAIGHT-IN APCH TO RWY 31R. I ALSO HEARD A BOEING JET ON THE ILS BACK COURSE APCH BEING CLRED TO LAND ON RWY 31L. I DID NOT KNOW HOW FAR BEHIND ME THE JET WAS WHEN IT WAS CLRED TO LAND. CLOSER TO THE ARPT, I CALLED FOR AND RECEIVED CLRNC TO LAND ON RWY 31R. AS I PROCEEDED TOWARDS THE RWY, WHICH I STILL COULD NOT SEE, VISIBILITY DETERIORATED TO ABOUT 2 MI IN BLOWING SNOW. I WAS ALREADY AT PATTERN ALT (1000 FT). I FOLLOWED A HWY (I-5) THAT I KNEW FROM EXPERIENCE WOULD LEAD ME DIRECTLY TO THE RWY. IT DID, AND I WAS EASILY ABLE TO INTERCEPT THE VASI AT PATTERN ALT AND LAND WITHOUT INCIDENT. I TUNED IN THE ATIS WHILE TAXIING. A 'SPECIAL OBSERVATION' INDICATED THAT THE FIELD WAS IFR WITH VISIBILITY OF 2 MI IN SNOW. THE TIME GIVEN FOR THE 'SPECIAL OBSERVATION' WAS SEVERAL MINS BEFORE I HAD LANDED. APPARENTLY A FAST- MOVING, LOCALIZED, UNFORECAST SNOW SQUALL (IN SEATTLE?!) HAD MOVED IN FROM LAKE WASHINGTON AND OBSCURED ONLY BOEING FIELD. NEARBY RENTON AND SEA-TAC REMAINED VFR. ANALYSIS: MY DECISION TO CONTINUE VFR IN CLASS D AIRSPACE TOWARDS A RWY I COULD NOT SEE WAS CLRLY AN ERROR. WHEN I REQUESTED AND WAS GRANTED CLRNC TO LAND FROM 3 MI AWAY, I STILL COULD NOT SEE THE RWY. I KNEW I WAS MAKING A DECISION, AND I KNEW THAT IT WAS PROBABLY THE WRONG ONE. HOWEVER, SOMEWHAT INCREDIBLY, IN THE HEAT OF THE MOMENT, I DID NOT IMMEDIATELY THINK OF WHAT THE RIGHT DECISION MIGHT BE, SO I BLUNDERED FORWARD. WHAT I SHOULD HAVE DONE: ON MY INITIAL CALL-UP FROM 6 MI AWAY, I SHOULD HAVE INDICATED TO THE TWR THAT THE FIELD DID NOT APPEAR TO BE VFR, AND TO PLEASE ADVISE. AT THAT TIME, I COULD EASILY HAVE REQUESTED A SPECIAL VFR. CERTAINLY UPON REQUESTING MY LNDG CLRNC, I SHOULD HAVE TOLD THE TWR THAT THE FIELD DID NOT APPEAR TO BE VFR. BY THAT POINT, ALREADY IN CLASS D, I COULD NOT HAVE OBTAINED A SPECIAL VFR CLRNC, BUT SOME SORT OF ARRANGEMENTS COULD HAVE BEEN MADE. IN ANY EVENT, I SHOULD HAVE EXECUTED A 180 DEG TURN UPON ENTERING IMC, SINCE I KNEW THAT VFR CONDITIONS EXISTED BEHIND ME, AND I DID NOT KNOW HOW BAD THE VISIBILITY WAS IN FRONT OF ME. IN CONDITIONS OF BLOWING SNOW, IT COULD EASILY HAVE DETERIORATED TO 1 MI OR LESS. IN GENERAL, MORE COM EARLIER ON WITH THE TWR WOULD HAVE PREVENTED ME FROM GETTING INTO THIS SIT. REASONS I DID NOT MAKE THE PROPER DECISIONS: THERE WAS NO PUSH-TO-TALK BUTTON ON THE R-HAND YOKE, FORCING ME TO USE THE HAND-HELD MIKE. THE MIKE HAD FALLEN TO THE FLOOR IN FRONT OF ME, AND, AS VISIBILITY DETERIORATED, I WAS CONCENTRATING ON MY FLYING AND HESITATED TO REACH DOWN AND PICK IT UP. MOREOVER, THE TWR HAD TOLD ME THAT THEY HAD DIFFICULTY HEARING MY XMISSIONS FROM THE MIKE (AND FROM THE CRUMMY ACFT RADIOS). I HESITATED TO EXECUTE A 180 DEG TURN OUT OF IMC BECAUSE I DID NOT KNOW THE POS OF THE BOEING JET BEHIND ME. IT MIGHT HAVE BEEN RIGHT ON MY TAIL, AND A BLIND 180 DEG TURN TOWARDS IT COULD HAVE BEEN DISASTROUS. MY STUDENT HAD TOLD ME THAT SHE NEEDED TO BE ON THE GND BY XA00 PM, AND TIME WAS RUNNING SHORT. AS A FAIRLY NEW CFI WITH A FAIRLY NEW STUDENT, I DID NOT WANT TO APPEAR THAT I WAS UNSURE OF WHAT TO DO. (HOWEVER, IN PREVIOUS SITS, THIS HAD NEVER BEEN A PROB FOR ME.) AFTER THIS FLT, MY STUDENT LEFT QUICKLY TO GET TO AN APPOINTMENT. BEFORE OUR LESSON THE NEXT DAY, HOWEVER, I GAVE HER A LENGTHY AND CANDID EVALUATION OF THE ERRORS IN JUDGEMENT I HAD MADE, AND WE HAD A VERY PRODUCTIVE DISCUSSION OF HUMAN FACTORS AND AVIATION DECISION-MAKING IN GENERAL.

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.