Date: 201303
Local time of day: 1201-1800
Location: ZZZ.Airport, US
Flight conditions: VMC
Weather elements / visibility: 100
Light: Daylight
Aircraft: Small Aircraft
Operator: Personal
Operating under: Part 91
Flight plan: None
Mission: Personal
Flight phase: Landing
ATC / advisory: UNICOM ZZZ
Reporter organization: Personal
Reporter function: Other / Unknown
Reporter qualification: Flight Crew Private
Second reporter function: Pilot Flying
Anomaly: Ground Event / Encounter Ground Strike - Aircraft; Inflight Event / Encounter Weather / Turbulence; Inflight Event / Encounter Loss Of Aircraft Control
Detector: Person Flight Crew
When detected: In-flight
Result: Aircraft Aircraft Damaged
Contributing factors: Weather; Human Factors; Aircraft
Primary problem: Ambiguous

Narrative: I was a passenger in the front cockpit of a 1934 Waco biplane. The pilot approached the Airport from the southeast and attempted to contact Unicom for an airport briefing but was unsuccessful. The pilot entered the pattern on a 45 from the southeast at pattern altitude and turned crosswind for Runway 35 at midfield. I saw at that point a plane take off on Runway 35 and depart to the north. I could see the wind sock and it was completely limp; indicating no wind. It showed that the wind direction was earlier favoring Runway 35. This was consistent with the wind direction when we left an hour earlier. The downwind; base and final legs were normal. Approximately 500 FT from the numbers and at an altitude of approximately 3 FT above the runway; the aircraft dropped abruptly to the ground and bounced. It felt like the wings had lost lift even though the aircraft had plenty of forward speed. The aircraft immediately veered sharply to the right and on the second bounce started to ground loop and was heading directly for the edge of the runway. There was no time to attempt a go around and if one had tried; it probably would have resulted in the aircraft running off the edge of the runway and flipping over on its back in the soft dirt. The aircraft skidded off to the east side of the runway. When the aircraft tires left the pavement and hit the soft dirt alongside the runway; the left gear leg dug into the dirt and the left gear folded under the fuselage; causing the left wing to slam onto the ground. The aircraft came to rest in the dirt facing the east with approximately 5 FT of its tail still remaining over the runway. The pilot stated that he had no rudder control at all prior to the ground loop. When we exited the aircraft we could feel a strong quartering tailwind from the southeast. I was surprised at the wind direction because the wind sock a few minutes before showed the situation to be calm. It is my opinion that we hit a thermal rising off of the runway that caused wind shear leading to the loss of lift; the bounce and the ground loop. There was no visual indication; such as rising dust; that there was a thermal; so there was no way to see and avoid it. I think that as we entered the thermal; it decreased our airspeed from wind coming directly from behind the aircraft; causing the aircraft to drop and as we proceeded through it; it caught us with a 90 degree crosswind that caused the ground loop. Damage to the airframe would have been much less severe if the runway edges were not 6 to 8 inches above grade and if the dirt was not so soft. It is possible that the aircraft would have just continued to skid along the dirt instead of dropping hard and digging in; if the ground was harder and there was no drop off from the pavement. Another factor that would have added to a safer situation would be if windsocks were located at each runway end. This is a large airport with only one windsock in the middle of the airport. A single windsock in the middle of the airport does not give a good indication of what the winds are doing a half mile away at the runway ends. Desert flying usually has windy conditions which at times can swirl in all directions. Windsocks are very important to flying aircraft with conventional gear safely.


Second narrative: I was the pilot of a 1934 Waco YMF-3. After touchdown and during the 'roll out' phase; the aircraft exited the east side of Runway 35 causing substantial damage to the aircraft but no injuries. Departure was in clear skies and wind from the northwest at 8-15 KTS and takeoff was uneventful. My passenger and I intended to fly in the vicinity for approximately an hour or so and return. After flying for approximately one hour; I decided to land at ZZZ to refuel prior to returning to home field; 10 miles away. I had approximately 1.8 hour fuel remaining. I monitored the CTAF from 20 miles southeast of the airport. No reporting traffic was heard; so I tuned ASOS to determine wind and runway from 10 miles out. ASOS reported wind 'variable' with no mention of speed or direction. I announced my intention to overfly the airport for a wind check. The windsock at the center of the airport indicated a light wind from the northwest. I announced entering downwind for Runway 35 and a full stop landing. When on final approach; the windsock at the end of Runway 35 indicated a light wind from the northwest but gusting a little. Control inputs confirmed a cross wind correction from the left to maintain runway centerline. Light turbulence was present but was not a factor. The approach speed was normal at 80-85 MPH. I allowed the aircraft to settle normally toward the runway while carrying a little power. Due to the long length of the runway; a wheel landing 2;000 FT down the runway was my intent. At an elevation of 2-3 FT above the runway the airplane suddenly dropped to the surface and bounced before the main gear tracked down the centerline. Suddenly the aircraft turned right toward the east side of the runway. I immediately applied full left rudder and brake and lowered the steerable tail wheel to the runway but the airplane never responded to the control inputs. At a slow speed but still skidding to the left; the left main gear dropped off the runway onto the soft sand. The left lower wing contacted the ground in a straight downward motion. The left main gear then collapsed from the side load resulting in damage to the left wing. There were no injuries to myself or my passenger. Upon exiting the aircraft the wind was from the southeast at 15 with higher gusts. This would be quartering tail wind. There were no visual cues during the approach or landing to suggest the existence of any adverse weather conditions such as a dust devil or windshear. After the incident; we remained partially on Runway 35 for about 30 minutes. We contacted the local FBO by telephone and they responded with a jeep. We towed the aircraft away from the runway to a position just short of the runway lights. Suggestions: 1) Place additional wind indicators at radial intervals along side of the runway to better detect windshear. When on final perhaps I could have detected the unsafe condition and abandoned the approach on landing. 2) Runway edge height is 8-10 inches in the accident area. Drop of height should be almost level. The soft sand is a hazard because of the increased likely hood of the aircraft coming to rest upside down after a runway excursion. This has happened several times at this airport. This greatly increases the chances of fire and injury.


Synopsis: Waco pilot and passenger report a ground loop during landing and a subsequent runway excursion with damage to the aircraft. A wind shift during landing and a significant surface drop when departing the runway edge were reported as factors in the incident.