When his copilot died, a pilot thought it was a joke and kept flying, report says.

A British copilot died while flying on June 29 and the pilot kept flying, thinking it was a joke, according to an Air Accidents Investigation Branch report.

The report released this month said the aircraft's pilot, who was qualified, wanted to fly from Blackpool Airport to another airfield but the crosswind was too high to fly on his own.

He asked the 57-year-old pilot to join him. The copilot said he'd go once he finished a trial lesson, the report said.

They took a 1978 Piper PA-28-161 that the agency calls the G-BORL in its report.

Shortly after takeoff, the copilot's head rolled back, the pilot recalled. The pilot said he knew the man well and thought he was pretending to take a nap, so he didn't think anything of it.

He flew the plane as planned but while making a turn, the copilot slumped over with his head on the pilot’s shoulder, the report said.

"The pilot still thought the (copilot) was just joking with him and continued to fly the approach," the agency said. "He landed normally on Runway 28 and started to taxi back to the apron. However, the (copilot) was still resting on his shoulder and was not responding, and the pilot (realized) something was wrong."

The pilot called the airport's fire crew over for help. The fire crew and air ambulance medical crew both tried to revive the man but they weren't able to save him.

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What happened to the copilot?

The 57-year-old man died from acute cardiac failure, the agency said.

"Toxicology showed no significant findings," the Air Accidents Investigation Branch said.

The man had a medical history of high blood pressure and was taking medication for it since 2002.

The Central Aviation Authority said the man likely suffered cardiac arrest as the plane took off. The authority also said he was overweight, a non-smoker and regularly saw a doctor for hypertension.

"His blood pressure had been treated for more than 10 years and was within regulatory limits," the report said.

Those who spoke to the victim on the morning of his death said he was his normal, cheerful self and there were no signs he wasn't feeling well.

"The three people who had flown with him for the trial lesson just prior to the incident flight said he seemed well and nothing abnormal had occurred," the agency wrote in its report.

How often do incidents like this happen?

The Air Accidents Investigation Branch said the risk of cardiac events in flight crew is never zero but that risk is managed by having more than one pilot on an aircraft at one time.

Previous reviews of reports dating back to 2005 showed three commercial flight incidents in the United Kingdom where a pilot suffered a heart attack; each time, copilots landed the planes safely.

Saleen Martin is a reporter on USA TODAY's NOW team. She is from Norfolk, Virginia – the 757 – and loves all things horror, witches, Christmas, and food. Follow her on Twitter at @Saleen_Martin or email her at sdmartin@usatoday.com.

This article originally appeared on USA TODAY: Pilot kept flying after instructor copilot died, thought it was a joke