Date: 201410
Local time of day: 0601-1200
Location: PAO.Airport, CA
Flight conditions: VMC
Weather elements / visibility: 100
Light: Daylight
Aircraft: Cessna 152
Operator: Personal
Operating under: Part 91
Flight plan: None
Mission: Training
Flight phase: Landing
Airspace: Class D PAO
ATC / advisory: Tower PAO
Second aircraft: Skyhawk 172/Cutlass 172
Reporter organization: Personal
Reporter function: Pilot Not Flying
Reporter qualification: Flight Crew Multiengine; Flight Crew Instrument; Flight Crew Commercial; Flight Crew Flight Instructor
Human factors: Situational Awareness; Confusion; Communication Breakdown
Anomaly: Conflict NMAC; Inflight Event / Encounter Wake Vortex Encounter
Detector: Person Flight Crew; Person Air Traffic Control
When detected: In-flight
Result: Air Traffic Control Issued Advisory / Alert; Air Traffic Control Issued New Clearance; Flight Crew Executed Go Around / Missed Approach; Flight Crew Took Evasive Action
Contributing factors: Airport; Human Factors
Primary problem: Human Factors

Narrative: My student and I were doing full-stop landing practice at Palo Alto. The visibility was in excess of 50 miles; the sky was clear; and the winds were very light; I believe less than 10 kts and less than 30 degrees off the centerline of runway 31. I believe that these excellent conditions led to a higher than normal amount of traffic in the area; as we had previously seen numerous airplanes in the practice area. The student was pre-solo and so I was doing most of the radio work and spotting traffic. Runway 31 was active. Numerous aircraft were in the pattern; probably 5 or more. We were on right downwind; runway 31. Right-hand traffic patterns are typical for runway 31 at Palo Alto. We were cleared to land (I think #3) behind a first 172 which was on the left downwind. I had difficulty spotting it and eventually saw what I thought was the traffic to follow. Typically; when the pattern is that crowded; the controller will call one's base to control the spacing. However; on this day; the controller was not doing so. Maintaining appropriate distance from the 172 I had spotted; I instructed the student to turn base. At this point we were over Shoreline Amphitheater; which is a very long final for runway 31. After turning right base; the controller shouted at us to turn left. I immediately took the controls and turned 90 degrees to the left. As I turned; I could see a second Cessna 172 just above us headed in the opposite direction. The Cessna was either on a left base or on an instrument approach to the same runway. The aircraft passed within 50 vertical feet of us and passed directly above us. We flew through its wake; and it caused the wings of our airplane to rock; probably 20 degrees of bank in each direction. I completed what was essentially a 270 degree turn and joined final for runway 31. The controller asked us if we were #1 or #2. I could see the second 172 immediately ahead of us and I responded that we were #2. However; the pilot of the second 172 responded that they were in fact #2 and gave the controller the sequence of airplanes on final. The pilot gave the N number of the 172 on short final (which was the first 172 that I had spotted when I was on downwind); stated that his N number was #2; and stated that I was #3. The first 172 landed. The second 172 asked the controller if they were cleared to land. The controller replied that the second 172 was cleared to land. At this point; we flew through the wake of the second 172 again; and again experienced our wings rocking to each side by about 20 degrees of bank. This was at approximately 400-500 feet AGL. There was negligible loss of altitude or airspeed and as an aerobatic pilot I did not feel that this particular incidence of wake turbulence was dangerous. However; it was not pleasant to experience. The second 172 landed and was rolling out. We were on short final and it became clear that the second 172 was not going to clear the runway in time. At approximately 100-200 feet AGL; I asked the controller if we were cleared to land. The controller replied by instructing us to go around and offset to the right; which is a typical go-around instruction at Palo Alto. We completed a right-hand traffic pattern. The controller called our base turn; and we landed without incident. I did not see the second 172 until it passed over us. I was not even aware there was a second 172 in the pattern; although this was the 172 we were supposed to follow. I believe that the contributing factors were several. First and foremost; the controller was not actively maintaining spacing between aircraft in the pattern by calling base turns. Second; there was a lack of awareness; certainly on my part; but perhaps also on the controller's part; as to exactly how many 172's were in the pattern. I say that the controller may not have been aware; since first; this near miss happened; and second; after it happened; he asked if we were #1 or #2; when in fact we were #3 behind 2 172's. This near miss possibly could have been prevented if I had clarified exactly who we were following and where they were; but it definitely would have been prevented had the controller followed the typical practice (at least at Palo Alto) of actively controlling spacing by calling base turns.Furthermore; the wake turbulence was disturbing. In retrospect; probably the best course of action in this regard would have been to go around far earlier. I did not expect to experience anything at all from the wake of a 172; it being a fairly light airplane. It is likely that the controller did not either; since the controller did not provide any such warnings and did not instruct us to go around until it was obvious that the second 172 was not going to clear the runway in time. All of us were slightly shaken up; including the controllers. I say this because both I and the second 172 had to ask for clearance to land on short final; and the second 172 pilot had to give the controllers the sequence of airplanes in the pattern. I am very grateful to the controller who instructed me to turn left. That was exactly the correct instruction. That put me heading away from the second 172. However; had I been 50 feet higher; we would have had a direct head-on collision regardless. The instruction would not have been in time to prevent a collision; as we passed directly under the second 172 with no horizontal clearance. The situation was avoidable. In addition to more emphasis on active control of aircraft spacing and providing better awareness of the number of airplanes in the pattern; perhaps training for controllers on dealing with the 120 seconds after a near miss would be beneficial.




Synopsis: A C-152 Instructor and his student on base leg for landing took prompt evasive action and avoided a C-172 that was flying on final. The pilot identified the wrong Cessna 172 as the traffic pointed out by the Tower. A timely alert from the tower as the two aircraft closed was instrumental in preventing a less benign outcome.