A U.K. man's instructor pilot slumped over in his seat during a flight last summer, but the man continued flying, believing his companion was pulling a prank on him.

Only upon landing the plane did the man realize his companion had suffered a heart attack and died during the short flight.

The incident was reported in a recent issue of the U.K. Air Accidents Investigation Branch. The names of the two men were not provided.

According to the report, the two men were flying a single-engine 1978 Piper Cherokee, a model commonly used for flight training.

The pilot, a member of the local flying club, had intended to fly from Blackpool Airport in Lancashire, England, to another airfield, "but when he arrived at the flying club and checked the latest wind, he decided the crosswind was above his personal limit to fly on his own.

"Still wanting to go flying so that he remained within the flying club’s recency requirements, the pilot asked an instructor if he would accompany him for a single circuit."

The 57-year-old instructor pilot agreed to go with him after he finished a trial lesson with three students.

When that lesson was completed, the instructor joined his friend in the Piper.

"The pilot recalled that during the taxi they were talking normally. He recalled telling the instructor he would keep the aircraft into wind for the power checks and the instructor replying, 'looks good, there is nothing behind you.'

"The pilot did not recall the instructor saying anything else after this point."

Soon after they took off, the pilot noticed the instructor's head had rolled back.

"The pilot knew the instructor well and thought he was just pretending to take a nap whilst the pilot flew the circuit, so he did not think anything was wrong at this stage," according to the report.

"He proceeded to fly the aircraft round the circuit. As he turned onto base leg, the instructor slumped over with his head resting on the pilot’s shoulder.

"The pilot still thought the instructor was just joking with him and continued to fly the approach. He landed normally on Runway 28 and started to taxi back to the apron.

"However, the instructor was still resting on his shoulder and was not responding, and the pilot [realized] something was wrong."

At that point, the flyer summoned a nearby emergency crew, which attempted to revive the instructor, "but he remained unresponsive and they were unable to save him."

Friends and acquaintances told investigators that the instructor "was his normal cheerful self" the morning of the incident. "[T]here were no indications that he was feeling unwell," according to the report.

"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."

A post-mortem report concluded that the instructor had died of acute cardiac failure.

"His coronary arteries showed diffuse atheromatous disease (a condition where the arteries become clogged with fatty substances) and there was a coronary thrombus (blood clot) occluding his left main stem artery," according to the report.

The instructor's last aviation medical exam had been about four months before his death. He'd had routine electrocardiograms, but "these were normal." He was known to have high blood pressure and elevated lipids, and he was overweight.

"The levels of coronary stenosis seen at post-mortem were disqualifying," according to the report. "Had he been symptomatic (angina) and investigated, the [Civil Aviation Authority] would not have certified him without treatment (i.e. stenting or bypass)."

"The CAA intends to review the circumstance of this incident at their cardiac panel to determine if anything can be learnt and if any changes should be made to the current guidance."

This article appeared originally on The Western Journal.