A flight from London to Chicago declared an emergency after a sudden and steep descent of 28,000 feet over Ireland and was forced to turn back to Britain.

一架从伦敦飞往芝加哥的航班在飞越爱尔兰上空时突然急剧下降28000英尺，随后宣布进入紧急状态，被迫折返英国。

British Airways flight BA295 was bound for Chicago's O'Hare airport but after a "technical issue" during which oxygen masks were deployed from the ceiling, the plane landed safely back at London Heathrow.

英国航空BA295航班原定飞往芝加哥奥黑尔机场，但在发生“技术问题”、舱顶氧气面罩弹出后，飞机安全降落在伦敦希思罗机场。

The aircraft, a Boeing 777-200ER, had departed Heathrow at 12.14pm on Monday for its scheduled transatlantic flight, and an hour into the journey had ascended to its cruising altitude of 37,000 feet.

这架波音777-200ER客机于周一下午12时14分从希思罗机场起飞，执行其定期跨大西洋航班，飞行一小时后已爬升至37000英尺的巡航高度。

According to passengers, the plane then encountered turbulence moments before the masks dropped, prompting "uncertainty" among those on board.

据乘客描述，氧气面罩弹出前，飞机遇到了颠簸，机上人员因此感到“不安”。

Pilots descended to below 10,000 feet and issued a 7700 emergency squawk to air traffic control – the international general emergency code – and made a U-turn to head back towards England.

飞行员将高度降至10000英尺以下，并向空中交通管制发出7700紧急代码——即国际通用紧急代码——随后掉头飞回英格兰方向。

Flight-tracking services showed the aircraft flying in a looping holding pattern over the Bristol Channel between Pembrokeshire and North Devon as the plane burnt off fuel in order to lower its weight, allowing the pilots to make a normal landing just after 5pm.

航班追踪服务显示，该飞机在彭布罗克郡和北德文郡之间的布里斯托尔海峡上空盘旋等待，以消耗燃油减轻重量，从而使飞行员能够在下午5时刚过正常降落。

Passenger Tom Nicholls said there was a "sudden bit of turbulence" before the emergency was declared and that the quick descent to 9,000ft hadn't been too uncomfortable.

乘客汤姆·尼科尔斯表示，在宣布紧急状态前出现了“一阵突然的颠簸”，而迅速下降至9000英尺的过程并不太难受。

He said: "The plane adjusted but it didn't feel like it was descending rapidly. I'd say the pilots did a very good job.

他说：“飞机进行了调整，但感觉并不是在急速下降。 我认为飞行员做得非常好。”

"The oxygen masks popped out soon after and there was a bit of uncertainty onboard. The couple in front couldn't get to theirs but by the time they'd found a spare seat with a mask, the captain announced we were below 10,000ft so they were not needed."

“氧气面罩随后弹出，机上出现了一些不安情绪。 前面那对夫妇够不到自己的面罩，但等他们找到一个有空位且带面罩的座位时，机长已宣布我们降至10000英尺以下，所以不需要使用了。”

A spokesperson for BA said: "The safety of our customers and crew is always our top priority, and the aircraft landed safely after our highly trained pilots returned to Heathrow following a technical issue.

英航发言人表示：“客户和机组人员的安全始终是我们的首要任务。在出现技术问题后，我们训练有素的飞行员将飞机返回希思罗机场并安全降落。”

"Customers disembarked the aircraft normally and our teams are working to get their travel plans back on track as quickly as possible."

“乘客正常下机，我们的团队正在努力尽快让他们的出行计划重回正轨。”

Photographs taken by passengers and shared on social media showed oxygen masks dangling from the ceiling as the plane made the return journey.

乘客拍摄并在社交媒体上分享的照片显示，飞机返航途中，氧气面罩从舱顶垂下。

A rapid descent to below 10,000 feet and a 7700 emergency squawk are routinely associated with aircraft experiencing cabin depressurisation but the official cause of the emergency has yet to be confirmed by BA.

迅速下降至10000英尺以下并发出7700紧急代码，通常与飞机客舱失压有关，但英航尚未确认此次紧急状态的官方原因。

The Boeing 777-200ER is one of BA's oldest planes in service, having been delivered to the carrier almost 30 years ago – in July 1997. Live streams showed the aircraft making its descent and safe landing back at Heathrow.

这架波音777-200ER是英航在役机队中最老的飞机之一，交付给该公司已近30年——于1997年7月交付。 直播画面显示该飞机下降并安全降落在希思罗机场。

Many passengers have been booked on to new flights departing on Tuesday.

许多乘客已被安排搭乘周二起飞的新航班。