Narrative:

During a soft-field takeoff in a tailwheel lsa from the overrun area of runway 14 I overflew an aircraft taxiing on runway 32 near the 14 threshold. I failed to check that the runway was clear prior to starting my takeoff run. I did not see the other aircraft until after liftoff due to the nose-high attitude. Because my transmitter was set to the wrong frequency; the other aircraft could not hear my transmissions.this event occurred during clear weather with a light crosswind. This airport is located [adjacent to] ZZZ1. I am based at ZZZ; a public-use grass airport with one 2;400 foot long runway. Runway 14 has a 1;000 foot overrun and a right-hand traffic pattern. The runway and taxiway were mowed; however there was long cut grass on the overrun for runway 14 that required a rolling soft-field takeoff. I started my takeoff about 300 feet into the overrun to allowed liftoff before the threshold.I made a series of mistakes. First; prior to taxiing I spent about 5 minutes on my hangar pad to get the engine oil temperature up; check ATIS; and link my kneeboard pc to ads-B. During that time I set my radio to monitor the tower frequency at ZZZ1 and to transmit on multicom. At some point I flipped the frequency so that I was transmitting on tower and monitoring the multicom frequency. As a result; any transmission by the tower would block my receiving 122.9 and aircraft in the pattern at ZZZ1 could not hear my transmissions.second; as I taxied I heard an aircraft inbound from the south for a right downwind to runway 14. I focused on locating the inbound aircraft. I stopped on the taxiway perpendicular to the runway for my pre-takeoff check and scanned my laptop ads-B display and the downwind for the incoming traffic. I turned right onto the runway overrun and checked for incoming traffic while back-taxing. Then I made a rolling 180 to lineup on 14. During the taxi and turn I scanned the approach to runway 14 and the downwind looking for the inbound traffic; I did not see the aircraft taxing on the runway 32 until I lowered the nose to best angle climb speed.finally; this event occurred because I failed to do either a complete pre-takeoff check or a line-up check. The pre-takeoff checklist includes a check that the radio is on the correct frequency. Had I done that item; the aircraft on the runway 32 could have heard my transmission that I was departing on runway 14. The line-up check includes a check of the runway ahead. When lightly loaded this aircraft takes off in a very nose-high attitude. This is a known issue that should have been addressed by scanning down the runway during the 180 and by s-turns early in the take-off run. I didn't do either. The fact that this is my home airport and there is usually no weekday traffic contributed to my sloppy procedure.

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Original NASA ASRS Text

Title: Rans S20 pilot reported that he did not check if the runway was clear prior to takeoff causing a NMAC right after liftoff.

Narrative: During a soft-field takeoff in a tailwheel LSA from the overrun area of runway 14 I overflew an aircraft taxiing on runway 32 near the 14 threshold. I failed to check that the runway was clear prior to starting my takeoff run. I did not see the other aircraft until after liftoff due to the nose-high attitude. Because my transmitter was set to the wrong frequency; the other aircraft could not hear my transmissions.This event occurred during clear weather with a light crosswind. This airport is located [adjacent to] ZZZ1. I am based at ZZZ; a public-use grass airport with one 2;400 foot long runway. Runway 14 has a 1;000 foot overrun and a right-hand traffic pattern. The runway and taxiway were mowed; however there was long cut grass on the overrun for runway 14 that required a rolling soft-field takeoff. I started my takeoff about 300 feet into the overrun to allowed liftoff before the threshold.I made a series of mistakes. First; prior to taxiing I spent about 5 minutes on my hangar pad to get the engine oil temperature up; check ATIS; and link my kneeboard PC to ADS-B. During that time I set my radio to monitor the tower frequency at ZZZ1 and to transmit on multicom. At some point I flipped the frequency so that I was transmitting on tower and monitoring the multicom frequency. As a result; any transmission by the Tower would block my receiving 122.9 and aircraft in the pattern at ZZZ1 could not hear my transmissions.Second; as I taxied I heard an aircraft inbound from the south for a right downwind to runway 14. I focused on locating the inbound aircraft. I stopped on the taxiway perpendicular to the runway for my pre-takeoff check and scanned my laptop ADS-B display and the downwind for the incoming traffic. I turned right onto the runway overrun and checked for incoming traffic while back-taxing. Then I made a rolling 180 to lineup on 14. During the taxi and turn I scanned the approach to runway 14 and the downwind looking for the inbound traffic; I did not see the aircraft taxing on the runway 32 until I lowered the nose to best angle climb speed.Finally; this event occurred because I failed to do either a complete pre-takeoff check or a line-up check. The pre-takeoff checklist includes a check that the radio is on the correct frequency. Had I done that item; the aircraft on the runway 32 could have heard my transmission that I was departing on runway 14. The line-up check includes a check of the runway ahead. When lightly loaded this aircraft takes off in a very nose-high attitude. This is a known issue that should have been addressed by scanning down the runway during the 180 and by s-turns early in the take-off run. I didn't do either. The fact that this is my home airport and there is usually no weekday traffic contributed to my sloppy procedure.

Data retrieved from NASA's ASRS site 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.