Investigators are just beginning the lengthy process of determining why a business jet plummeted from the sky in Florida after encountering a thunderstorm and slammed into the ground with such force that it created a crater and shattered the plane. The experts at the National Transportation Safety Board will lead the investigation into the crash that killed all nine people abord the Learjet, but it will likely take more than a year to determine exactly what caused this tragedy.

Dramatic videos from witnesses — combined with the disturbing final radio transmissions as the pilots realize their fate — will give investigators important clues. The cockpit voice recorder would also help if investigators can find it intact.

“Our mission is to understand not just what happened, but why it happened, and to recommend changes to prevent it from happening again,” NTSB member Tom Chapman said. Here's what investigators are doing now and what comes next:Investigators are gathering critical evidenceAn NTSB team will spend days collecting every piece of the plane they can find. Investigators said Tuesday that pieces of a key part of the tail called the elevator that controls the angle of the nose were found more than a mile away from the main crater. That confirms the plane started to break apart before impact.

Chapman said investigators are searching for the Learjet's cockpit voice recorder because it could provide crucial details about what the pilots were talking about as they lost control of the plane after it encountered turbulence and ice started to build up on the wings.“That will be very important data,” Chapman said. But being unable to find that recorder won't doom the investigation.

“Without it, our folks are very, very good. We’re still able to do some incredible detective work and determine how things transpired.”The co-pilot told air traffic controllers that the plane was being thrown up and down more than 700 feet (213 meters) as she asked them for a better route through the area. It's not clear why the pilots hadn't flown around the storms.

But torrential rains in Florida over the past week are making investigators' work more difficult. The crater was filling with rainwater that likely left some pieces of the plane submerged, and a utility pole had to be removed. The NTSB asked anyone who finds part of the plane to report it for investigators to collect.

Initial NTSB report takes about a monthTwo news conferences have provided some initial details. But the NTSB will spend most of the next month developing a preliminary report describing what happened. Crash evidence will be taken to a secure hanger where investigators can test intact components and even try to reassemble parts to get a better idea of what happened.

But the force of the crash and the fire destroyed much of the plane, so that will make investigators work harder. Retired airline pilot and aviation safety expert John Cox said he also doesn’t understand why the plane descended from its previous cruising altitude of 41,000 feet (12,497 meters) as it approached the storms. The pilots steered around a larger storm cell but appeared to head directly into a rapidly developing smaller one, Cox said.“If I’m looking at thunderstorms, I’d rather be at 41 than at 35. You’ve got a better view, you’re more likely to be on top of it, or at least, in the very wispy tops of it,” Cox said.

“I don’t understand why they came down.”Investigators will try to determine whether they knew that storm cell was there, what the plane’s weather radar showed and whether the pilots checked any other weather services. Pilot in Learjet crash that killed 9 in Florida was a husband, father and a devout ChristianPreliminary reports provide factual details but don't include any analysis or cause.

That takes much more time. Investigators will dig deeperWeather will be a key early focus of the investigation. NTSB experts will work with the National Weather Service and Federal Aviation Administration to get a better idea of what the plane encountered as it was cruising at 35000 feet (10,668 meters).Maps that overlay the flight path on top of colorful weather maps show the Learjet flying directly into a small red storm cell that worsened quickly. But the board considers everything that may have contributed to a crash.

Investigators will review maintenance records and any history of problems with the plane. They will also interview officials at the Upper Jets company that operated the flight as well as air traffic controllers and people who work at the Texas airport the plane took off from. Videos and photos shot by bystanders can also provide crucial clues about what happened. The NTSB will also collect copies of any surveillance footage that might show the crash. In certain high-profile crashes, the NTSB may also hold several days of investigative hearings where investigators can question key people involved to learn more and share details with the public as they did after last year's UPS plane crash.

The final report could take more than a yearGenerally, it takes 12-18 months for the NTSB to complete a crash investigation, but it can take longer in complicated cases.

NTSB's roughly 400 workers are pursuing over 1,200 active investigations. Final reports include details about what happened and explain probable causes. The NTSB also develops recommendations to prevent similar crashes and improve safety. But the independent agency doesn't have power to require those changes to be made.' She was like sunshine': Nathalia Gadelha Filgueiras' friend remembers co-pilot killed in Florida Learjet crashInstead, it is up to regulators like the FAA, the industry and Congress to adopt the NTSB recommendations.

But there is a long history of NTSB recommendations being ignored because regulators or the industry decide making the change would be more costly and cumbersome than it is worth. Even when the FAA or Congress agrees with the suggestions it might take years to approve new rules.