Rescue crews continued their search Tuesday for a downed chopper near Molokai by air and sea, but the whereabouts of the two on board remain unknown.
Multiple agencies are working together to conduct search efforts.
Tuesday morning, the Maui Fire Department's Air 1 recovered an uninflated life vest floating on the water's surface about 100 yards from shore and a mile east of Ilio Point, officials said.
The vest was eventually turned over to the Coast Guard for proper identification, and no other debris has been found.
Maui fire officials also said a man fishing Monday night at Moomomi Beach witnessed the aircraft go down. He described what he saw as "a red beacon of an aircraft" that descended rapidly to the ocean and then it disappeared in the direction of Molokai's Ilio point.
The chopper, which was on its way back to Honolulu with a flight student and instructor on board, was from Mauna Loa Helicopters. The company is also assisting in the search.
"Our thoughts and prayers are for the people involved and their families," said company President Benjamin Fouts. "You try to prepare in the training and do the best you can in the situation you're given."
Officials said debris and chemlights were located about one and half miles from shore, but it's unclear if the items were from missing helicopter.
Coast Guard officials were notified of the suspected downed helicopter at 7:26 p.m. Monday, when it vanished from radar.
Fouts said the two men left Honolulu about 6 p.m. Monday for a training flight to Molokai, and were supposed to return by 8 or 8:30 p.m.
There was no mayday call, according to Mauna Loa Helicopters.
"It's just so sad, but bad weather and nighttime, that's often a formula, a recipe for tragedies," said John Corboy, a Molokai pilot who owns a Robinson R-44. "I understand there was a lull maybe at 6 o'clock when they took off, but pretty soon it was gusting back up," he said.
Fouts said the flight school's standard policy is not to allow students to fly in winds above 25 knots, which is roughly 29 miles per hour.
The Coast Guard said that crews searching for the helicopter on Monday night dealt with 30 mph winds and 12 to 15-foot seas.
On Tuesday, rescue crews were working in less than ideal conditions, with 25 mph winds and 15-foot seas.
Company officials said the student on board the flight moved to Hawaii from California about a year ago, and is close to completing the school's Professional Pilot Program which is designed to help students earn five ratings and certificates.
His teacher, officials said, is one of the most experienced at the company and has been working for Mauna Loa Helicopters for at least two years.
Amanda Levasseur, Coast Guard Petty Officer 3rd class, said the helicopter is a Robinson R-44, a four-seat light helicopter.
Company officials says the R-44 is a good aircraft for training, but aviation attorney and pilot Rick Fried disagrees.
"These Robinsons are a very tricky helicopter," said Fried. "You need to be very experienced. Hughes, Bells, others, similar to that, are far easier."
Its tail number was confirmed as N820DF and, according to FAA records, it was manufactured in 2002.
In 2013, the same chopper was involved in a "precautionary landing" at Magic Island. It had a crack on the left door window, and no injuries were reported.
A Coast Guard airplane, helicopter and vessels are participating in the search along with a Navy helicopter and a Maui Fire Department chopper and ground crews.
The chopper search comes last than a year after a well-known attorney Gary Galiher and Honolulu realtor Keiko Kuroki were killed in a helicopter crash on Molokai. Weather is believed to be a factor in the crash.
In 2011, five people were killed when a tour helicopter crashed into a hillside on the east end of Molokai. Two newlyweds from Pennsylvania, a Canadian couple and the pilot were killed. Authorities said pilot error is to blame for the crash.