The flydubai jet may have lost both engines during its 18,000-foot plunge, aviation expert and pilot Steve Scheibner said. He also praised Capt Smit Machchhar and passengers whose brave actions helped avert a catastrophic crash.

The engines of a flydubai aircraft may not have been working when the plane plunged nearly 18,000 feet following an attack by its Omani co-pilot on the Indian captain, according to an aviation expert.

Speaking to British broadcaster Piers Morgan, retired US Navy and American Airlines pilot Steve Scheibner said information from reliable sources and videos of the incident indicate that both engines may have cut off during the aircraft’s steep descent.

"It seems as though both engines were not operating while they were in the midst of this dive and we're reporting on that because the emergency evacuation lights on the inside of the airplane illuminated," Scheibner said.

"There's only one way for those lights to illuminate in flight, and that's that both engines are not operating," he added.

Scheibner said the incident was even more remarkable because the off-duty pilots who entered the cockpit not only helped bring the aircraft out of its nosedive but also had to restart its engines amid the chaos.

The latest details follow the dramatic September 30 incident aboard flydubai Flight FZ1073, which was travelling from Dubai to Tel Aviv. Investigators said co-pilot Hamam al-Hammami attacked Indian Captain Smit Machchhar inside the cockpit with an axe in an attempt to take control of the aircraft in a "terrorist attack".

Flight data showed the Boeing 737 descending about 5,500 metres, or 18,000 feet, in roughly 30 seconds. However, at this point, it is not known for certain whether al-Hammami had damaged or manipulated the flight controls in a way that disengaged the autopilot and triggered the dive.

Passengers and others on board eventually intervened, subdued al-Hammami and helped remove the injured captain from the cockpit. The aircraft was diverted to Saudi Arabia, where it landed safely. Al-Hammami was handed over to authorities.

Scheibner praised Capt Machchhar and the passengers for their bravery and quick-thinking that averted a disaster.

"Captain Schmidt is an absolute hero. He's the first hero amongst many on that flight. He had the presence of mind while he's fighting for his life, by the way, being attacked with the crash axe in the airplane to reach back," he said.

Capt Scheibner explained that the Boeing 737 cockpit door could be opened from inside, allowing a woman near the front toilet to see the struggle. She alerted her husband, who rushed to help before other passengers moved toward the cockpit.

He said the response reflected a major change in passenger behaviour since the 9/11 attacks. He said passengers now understand they may need to intervene when an aircraft is under threat.

"And so they worked through that rather quickly, pulled out the captain, and started getting him medical attention while they're fighting, fighting with the co-pilot at the same time that this airplane is in a steep dive. All of this is absolutely amazing." Meanwhile, more details of the flydubai attack continue to emerge. The investigation so far indicated that al-Hammami had extreme Islamist views, had acted alone, and planned to crash the plane into Ben Gurion Airport or another building in Tel Aviv.

Two Israeli officials with knowledge of the investigation also told Reuters that al-Hammami said during questioning that he had planned the attack before being hired by flydubai.