Horrific Learjet crash still a mystery. Here's when we'll know more - USA Today

It's been five days since a business jet raced nose-down toward the ground and crashed near a South Florida community, killing all nine people on board, and it may be much longer until the nation learns why it happened.

Federal investigators have warned that the investigation will be complicated and lengthy, made even more difficult because much of the plane was totally destroyed by the impact.

“The force of this impact very, very severely damaged the remnants of the wreckage,” National Transportation Safety Board member Tom Chapman said.

The Learjet 60, bound for the Bahamas from Austin, Texas, crashed just before 1 p.m. in Palm Beach County. The plane plunged to the ground at more than 300 mph and exploded in a fireball, forcing the evacuation of at least 600 people living nearby. Everyone aboard the plane was killed – a pilot, co-pilot and seven passengers, including a family of four.

The crash was documented in horrific audio that captured the final moments of the flight crew, who described hurtling toward earth in an out-of-control plane. At the crash site, dash cam video shows the plane hitting the ground in a fireball.

Experts say investigators will likely zero in on how the plane found itself in a precarious, high-altitude situation in bad weather, and why it suddenly plummeted. Some pointed to the dangerous effects that icing and turbulence can have on jets. Others wondered whether the aircraft experienced an infamously deadly condition called "Mach tuck," where jets speed toward earth nose-down with almost no ability to avert disaster.

But officials stress that the investigation is in its early days, and they do not yet have information about what caused the crash.

The National Transportation Safety Board, the agency charged with investigating civil transportation accidents, is leading the sprawling probe into the deadly Nov. 1 crash. Investigators will review everything from remnants of the plane to maintenance records to potential audio recordings from the cockpit.

But while “significant evidence” has been recovered, Chapman said months of challenging analysis and reviews lay ahead.

“Our mission is to understand not just what happened, but why it happened and to recommend changes to prevent it from happening again," he told reporters.

The NTSB investigates 1,200 aviation accidents and incidents a year, according to the agency’s website. Each case generally follows the same process, beginning with on-site investigations and lab analysis before a probable cause is determined and a final report is released.

During the initial stage of an investigation, NTSB personnel scour the accident site for evidence. In aviation probes, this can include cockpit recordings and recovered parts of the aircraft. Investigators also collect flight logs and maintenance records and conduct personal interviews.

Roughly a month after an accident, the NTSB typically releases a preliminary report containing only factual information collected on scene, according to the agency. The preliminary report "will not contain analysis or contain a finding of probable cause," the NTSB says on its website.

Next, specialists work to piece together a sequence of events and determine what happened to cause the accident. The team will then draft a thorough report laying out what investigators believe occurred and zeroing in on a probable cause. Once the final accident investigation report is adopted, the final copy of the report will be released to the public.

The NTSB says it aims to complete investigations within 12 to 24 months, but the time frame can change depending on the complexity of the investigation and the workload of NTSB investigators.

Since the crash, investigators have found several key pieces of the Learjet. On Nov. 5, the NTSB said in an update that crews recovered a piece of an engine at the crash site, where excavation work began a day earlier.

This comes after Chapman said components of the plane were found as far as 1.3 to 3.8 miles away from where it crashed. Among the items recovered was the plane’s left elevator, a movable control system that manages the pitch of the aircraft, pointing the nose up or down.

Chapman said NTSB crews, working closely with local, state and other federal partners, will recover as much of the aircraft as possible before laying out the pieces to identify the shape, form and location of the various components.

“Sometimes that helps us identify something that may have occurred, which may not be obvious,” Chapman said.

But that method will be hampered by the immense amount of damage caused by the high-speed impact. Some experts estimate that the plane hit the ground at more than 300 mph. Upon impact, the plane exploded into a ball of fire and sent debris – including parts of the plane and chunks of asphalt – toward nearby homes and roadways.

Chapman said crews had begun to remove water from the crater that formed when the plane slammed into the ground. Investigators previously said it would take several days to recover the wreckage from the impact crater, which was filled with water due to the weather, and the wide swath of debris left behind by the plane.

One key target of the search is the cockpit voice recorder, also known as a black box. Chapman said records indicate such a device was installed on the aircraft at some point, but investigators don’t know whether it was still on board before the crash.

Chapman also said investigators have begun reviewing a trove of videos of the crash that could help them understand the state of the aircraft as it plummeted toward the ground. The agency has asked witnesses to provide videos they have to investigators. Authorities have also asked residents not to touch any debris they come across and report any potential findings.

The FAA said the Learjet 60 departed Austin-Bergstrom International Airport at 10:37 a.m. ET and was en route to the Bahamas when it crashed about two hours later.

Moments before the crash, the crew reported that they were at about 35,000 feet and the temperature outside was -53°F, Chapman, the NTSB member, said. A person in the cockpit said the crew was "managing the ice," encountering "moderate" turbulence and seeking "better rides," according to air traffic control audio.

On its flight path, the plane had encountered severe storms that had triggered flood warnings across Palm Beach County. The crew member reported taking on “precipitation” and requested a new altitude of 37,000 feet. Air traffic control in Miami Center soon gave the aircraft permission to climb.

Less than a minute later, the crew member issued a mayday call and reported that the aircraft was descending at 10,000 feet per minute. Seconds later, the person declared an emergency and said the descent rate had accelerated to 20,000 feet per minute.

"We're going to crash into the ground," the person said. About 35 seconds after the initial distress call, the last cockpit transmission was: "We're out of time."

Flight tracking website Flightradar24 said data showed the vertical descent rate at one point exceeding 32,000 feet per minute. Videos captured the jet nosediving into the ground near the entrance to a mobile home community before erupting into flames.

Family members identified the passengers as Adam Robinson, 45; his wife, Helen Sharp, 40; their children, Emma, 4, and Charlie, 2; the children's nanny, Anita Maria Cetina; and another couple, Rachael Reed and Charmi Fehr.

Relatives also identified one of the pilots as Nathalia Filgueiras, 20. The aircraft's captain was identified as Jeff Gregory, 55, by his former employer, East Coast Jets, as well as CBS News and the New York Post.