An artwork conveying well wishes for the passengers and crew of the missing Malaysia Airlines Flight MH370 at a viewing gallery in Kuala Lumpur International Airport. Photo: Edgar Su/Reuters

Whoever reached across the dimly lit cockpit of a Malaysia Airlines jet and clicked off a transponder to make Flight MH370 vanish from controllers’ radars flew the plane into a navigational and technical black hole.

By choosing that exact place and time to vanish into radar darkness with 238 others on board, the person – presumed to be a pilot or a passenger with advanced knowledge – appears to have acted only after meticulous planning, according to aviation experts.

Understanding the sequence that led to the unprecedented plane hunt widening across two vast tracts of territory north and south of the Equator is key to grasping the motives of what Malaysian authorities suspect was hijacking or sabotage.

By signing off from Malaysian airspace at 1.19am on March 8 (1719 GMT March 7) with a casual “all right, good night” rather than the crisp radio drill advocated in pilot training, a person now believed to be the co-pilot gave no hint of anything unusual.

Two minutes later, at 1.21am local time, the transponder – a device identifying jets to ground controllers – was turned off in a move that experts say could reveal a careful sequence.

Every action taken by the person who was piloting the aircraft appears to be a deliberate one. It is almost like a pilot’s checklist

“Every action taken by the person who was piloting the aircraft appears to be a deliberate one. It is almost like a pilot’s checklist,” said one senior captain from an Asian carrier with experience of jets, including the Boeing 777.

The radio call does not prove it was the co-pilot who turned off the transponder. Pilots say the usual practice is that the pilot not in control of the plane talks on the radio.

A young man comforts a crying girl during a special prayer for the passengers of the missing Malaysia Airlines flight MH370 in central Kuala Lumpur. Photo: Damir Sagolj/Reuters

Police have searched the premises of both the captain and co-pilot and are checking the backgrounds of all passengers.

But whoever turned the transponder to ‘off’ did so at a vulnerable point between two airspace sectors when Malaysian and Vietnamese controllers could easily assume the airplane was each others’ responsibility.

“The predictable effect was to delay the raising of the alarm by either party,” David Learmount, operations and safety editor at Flight International, wrote in an industry blog.

That mirrors delays in noticing something was wrong when an Air France jet disappeared over the Atlantic in 2009 with 228 people on board, a gap blamed on confusion between controllers.

Yet whereas the Rio-Paris disaster was later traced to pilot error, the suspected kidnapping of MH370’s passengers and crew was carried out with either skill or bizarre coincidences.

Whether or not pilots knew it, the jet was just then in a technically obscure sweet spot, according to a top radar expert.

Air traffic controllers use secondary radar which works by talking to the transponder. Some air traffic control systems also blend in some primary radar, which uses a simple echo. But primary radar signals fade faster than secondary ones, meaning even a residual blip would have vanished for controllers and even military radar may have found it difficult to identify the 777 from other ghostly blips, said radar expert Hans Weber.

“Turning off the transponder indicates this person was highly trained,” said Weber, of consultancy Tecop International.

The overnight flight to Beijing from Kuala Lumpur is packed year-round with business people, Chinese tourists and students, attracted in part by code-sharing deals, regular travellers say.

The lockdown of MH370 may have begun as early as 40 minutes into the flight at a point when meals are being hurriedly served in time to get trays cleared and lights dimmed for the night.

“It was a red-eye flight. Most people – the passengers and the crew – just want to rest,” a Malaysia Airlines stewardess said. “Unless there was a reason to panic, if someone had taken control of the aircraft, they would not have noticed anything.”

At some point between 1.07am and 1.37am, investigators believe someone switched off another system called ACARS designed to transmit maintenance data back to the ground.

The explanation of the timing has shifted after Malaysian officials initially said it was turned off before the pilot last spoke at 1.19am. But it could have been done later as well, although before 1.37am, when the system was to make another transmission, which it did not.

By itself, switching off ACARS was unusual but would not necessarily have raised alarms at the airline and the passengers would not have known something was amiss, said some of the six pilots contacted by Reuters, none of whom agreed to be named.

“Occasionally, there are gaps in the communications systems and the guys in ground operations may not think much of it initially. It would be a while before they try to find out what was wrong,” said one captain with an Asian carrier.

Cutting the datalink would not have been easy. Instructions are not in the Flight Crew Operating Manual, one pilot said.

Circuit-breakers used to disable the system are in a bay reached through a hatch in the floor next to the left-hand front exit, close to a galley used to prepare meals.

After the transponder was turned off, the northeast-bound jet took a northwestern route from the sea off Kota Bahru in eastern Malaysia to Penang Island. It was last detected on military radar around 200 miles northwest of Penang.

The airline said it had reconstructed the event in a simulator to try to figure out how the jet vanished and kept flying for what may have been more than seven hours.

Pilots say whoever was then in control may have kept the radio on in silent mode to hear what was going on around him, but would have avoided restarting the transponder at all costs.

“That would immediately make the aircraft visible ... like a bright light. Your registration, height, altitude and speed would all become visible,” said an airline captain.

Although investigators have refused to be drawn into theories, few in the industry believe a 250-tonne passenger jet could run amok without expert skills or preparation.

“Whoever did this must have had lots of aircraft knowledge, would have deliberately planned this, had nerves of steel to be confident enough to get through primary radar without being detected and been confident enough to control an aircraft full of people,” a veteran airline captain said.