Narrative:

While in cruise eastbound at 3;000 ft MSL near vernonia; the garmin 530 alerted me to traffic very close by at the same altitude. I acquired the traffic visually at about 11 o'clock; about 50 ft above us. It was a small cessna single engine. We were converging at about a 30-45 deg angle both headed easterly. I made a slight change in course and altitude to ensure separation. Due to the position of the other traffic and the angle; I would likely not have seen the aircraft if not for the traffic alert. (It required me to lower my head about 12 inches and look up and left to get acquire him visually). Since we had a patient on board; there was not a crewmember in the left front seat to assist with scanning that side. This was a very close call. I cannot say for certain that a collision would have occurred if not for the traffic alert; but it was the closest call I've had in my career. Our aircraft is equipped with tis; and we were receiving service because we were close enough to pdx. If we were farther away; no alert would have been received. I do not know if the airplane ever saw us. I was monitoring hio tower on one radio and CTAF for vernonia on the other; and never heard an aircraft which I could positively say was the one I was near. Even with a very vigilant scan; this aircraft may have been undetected by me due to the angle at which we [were] converging; and the visibility offered in the helicopter cockpit.

Related reports:

Google
 

Original NASA ASRS Text

Title: Helicopter pilot near 05S at 3;000 FT reports a NMAC with a single engine Cessna. The approaching Cessna was obscured by the cockpit structure and not detected until the TIS alerted.

Narrative: While in cruise eastbound at 3;000 FT MSL near Vernonia; the Garmin 530 alerted me to traffic very close by at the same altitude. I acquired the traffic visually at about 11 o'clock; about 50 FT above us. It was a small Cessna single engine. We were converging at about a 30-45 deg angle both headed easterly. I made a slight change in course and altitude to ensure separation. Due to the position of the other traffic and the angle; I would likely not have seen the aircraft if not for the traffic alert. (It required me to lower my head about 12 inches and look up and left to get acquire him visually). Since we had a patient on board; there was not a crewmember in the left front seat to assist with scanning that side. This was a very close call. I cannot say for certain that a collision would have occurred if not for the Traffic Alert; but it was the closest call I've had in my career. Our aircraft is equipped with TIS; and we were receiving service because we were close enough to PDX. If we were farther away; no alert would have been received. I do not know if the airplane ever saw us. I was monitoring HIO Tower on one radio and CTAF for Vernonia on the other; and never heard an aircraft which I could positively say was the one I was near. Even with a very vigilant scan; this aircraft may have been undetected by me due to the angle at which we [were] converging; and the visibility offered in the helicopter cockpit.

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.