A California couple were identified Monday as the victims of a weekend airplane crash in Worth County.

Authorities said Henry Manwarren, 71, and his wife, Beth Arlene Manwarren, 69, were killed instantly Saturday when their single-engine aircraft plunged into a soybean field north of Grafton.

The couple, from Merced, Calif., were en route to Oshkosh, Wis., for a vintage air show in a 1959 Beechcraft V-35 that went down about 1:30 p.m.

There were no witnesses to the crash, Worth County Sheriff David Gentz said. Federal investigators said Monday that bad weather likely contributed to the crash. A severe thunderstorm with lightning and high winds passed through the area shortly before the wreckage was spotted, Gentz said.

MASON CITY - Henry and Beth Manwarren went to Oshkosh, Wis., once a year. They would fly from Merced, Calif., stopping to see relatives along the way.

"It was an annual event for them," said Jamie Tucker of Tulsa, Okla., their granddaughter. "It was their main, yearly vacation. They have lots of friends there and they would always stop and visit relatives."

Funeral services for the couple will be held at 11 a.m. Saturday at the United Methodist Church in Lyons, Kan.

"They both grew up around there and we have family there," Tucker said. "That's where they met. They both went to Lyons High School and they were married at the Methodist church."

Tucker last spoke with her grandfather two weeks ago, on his birthday. And he talked of making the annual flight to Oshkosh.

"He has flown around weather so many times," Tucker said. She also noted that her grandmother was a licensed pilot.

"I'm going to school to be a pilot right now," said the 24-year-old granddaughter. "So it is hard for me to hear all of this.

"But I went to class this morning and it is not going to be a discouragement for me. I'm going to finish because it is something he would want me to do. I'll do it in memory of them."

MASON CITY - Neither of the Fixed Base Operators (FBOs) at the Mason City airport heard any radio traffic from the pilot of the airplane that crashed near Grafton Saturday, killing two people.

That would be expected in the case of an airplane passing through the area with no intention of landing or seeking information from the airport.

Henry Manwarren of Merced, Calif., was flying according to "visual flight rules" (VFR) which does not require him to be in radio contact with anyone.

If weather conditions and visibility were bad enough, Manwarren could have filed a flight plan to fly to his destination relying on instruments. He then would have been flying IFR, instrument flight rules.

That was not the case and no one knows if he was flying close to the storm activity in the area or if weather played a role in his crash.

The Mason City airport does not have a control tower to monitor and control flight operations because "the level of activity doesn't warrant the cost of operating a control tower," said Duane Haataja, airport manager.

The FAA does a cost/benefit study in deciding whether a control tower is needed and an airport usually has to have at least 75,000-100,000 landings and takeoffs to be considered a candidate. Haataja estimates the Mason City airport had about 40,000 operations last year.

In good weather, pilots flying into and out of the airport broadcast their intentions and/or seek information from an FBO on the ground or other pilots by broadcasting on unicom radio. The airport's frequency is 123.0 megahertz. Pilots flying within 30 miles of the airport typically use this frequency. The pilots may be seeking airport or air traffic advisories, Haataja said.

"Once near the airport pilots are required to report their position and required to listen," he said. "It's see and be seen; hear and be heard."

For pilots flying IFR, wanting to land at Mason City using instruments instead of visual references, they can do so but they will be controlled by radio out of the "Minneapolis Center," said Jerry Dwyer, long-time FBO at the airport. Dwyer was referring to the nearest of 21 national air route traffic control centers.

"When flying, we actually talk to Minneapolis Center and they handle us. Unicom does not control anybody. It's an advisory situation," he said.

"We did have a control tower structure years ago, but the FAA used it for weather," Dwyer said. The FAA kept raising the requirements for having a staffed control tower and Mason City never met the criteria.

Actually, flying is far safer today than it was 25-30 years ago, Dwyer said. Airplanes flying under control used to be spaced 5 nautical miles apart but are now spaced 20 miles, he said. Computers and good communications has added to the margins of safety he said.

"You can fly 86 miles in an airplane with the same exposure to an accident as you would driving one mile in your car," he said.

Dwyer wasn't sure when the last fatal plane crash occurred in North Iowa.

"It was a long time ago. Maybe when they were building I-35. I'd say 30-to-35 years ago."

Reach David Krotz at 421-0556 or david.krotz@globegazette.com.