ANCHORAGE -

The National Transportation Safety Board is still in the early phases of its investigation into the Nov. 29 crash of a Cessna 208 Caravan that killed four people.

But a Lower 48 law firm said the plane should not have been in the air the day it went down because it did not have an adequate de-icing system.  

Ladd Sanger, an aviation lawyer who works for Texas-based Slack and Davis, has been part of litigation cases involving Cessna 208 icing problems in the past.

He said based on preliminary information indicates Friday's crash near St. Mary's suggests the same problem occurred in the Western Alaska crash.

Sanger said Cessna changed the design of the caravan's ice protection system, but there are at least 5,000 planes across the country that have not been retrofitted with the safety upgrades. 

According to a 2011 NTSB report, there have been 47 fatalities involving Cessna 208 Caravans that were covered in ice: including 10 from a 2001 Pen Air crash in Dillingham.

Sanger said he wonders why Cessna and Hageland Aviation services allowed that plane to fly. 

"It's one thing to have an airplane down in the Caribbean, you don't even need an deicing system at all," he said. "But when operating that plane like Hageland is in Alaska, where you're certain to have low visibility and icy conditions on a regular basis, you really need to have the most sophisticated up to date and reliable deicing system." 

Era Alaska owns Hageland and issued a statement today: "We look forward to providing pertinent information to the NTSB and all local, state and federal agencies. 

"We will not engage in speculation until the investigation is complete, as it may impact the inquiry into the accident."

15 air carriers in Alaska that fly Cessna aircraft declined to comment on their own safety modifications.