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.

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Original NASA ASRS Text

Title: 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.

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.

Data retrieved from NASA's ASRS site as of July 2013 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.