( CNN ) -- Two of the four survivors of this week 's crash on an Alaska mountainside were well enough to talk with government officials looking into the cause of the crash , National Transportation Safety Board ( NTSB ) Chairwoman Deborah Hersman told reporters on Friday . Both survivors recalled the pilot giving a safety briefing before the flight , she said . The survivor who sat in the front seat reported falling asleep almost immediately after the plane took off and waking up after the crash . The other survivor told investigators `` they were flying along and then just stopped flying , '' according to Hersman , who did not say which of the four survivors investigators spoke with . Five people died in the Monday night crash , including former U.S. Sen. Ted Stevens . The family of experienced pilot Terry Smith , who was killed in the accident , released a statement Friday saying , `` This is a time of great sorrow for our family . Our hearts and prayers go out to the survivors and the family and friends of all those affected by this tremendous loss . '' Smith had been involved in a prior accident , in 1997 , said Hersman . No one was injured in that accident , in which the plane nosed over during landing . The incident was chalked up to the pilot 's failure to maintain control , she said . Those killed in the crash could not have been saved even if rescue teams had arrived at the site immediately , officials said . The autopsies found the deaths were the result of blunt force trauma , said Greg Wilkinson , an official at the Medical Examiner 's office . He said the state medical examiner , Dr. Katherine Raven , found the injuries to be consistent with this type of crash . Raven also found that the injuries were not survivable , he said . Meanwhile , the condition of former NASA chief Sean O'Keefe has been upgraded from critical to serious , according to the Providence Alaska Medical Center . He was the most seriously injured of the four survivors . `` Sean is making significant improvements , '' an O'Keefe family spokesman said on Friday . `` ... It does not appear that any of Sean 's injuries require surgery . And we are encouraged by medical reports indicating that Sean 's injuries are not life-threatening . '' O'Keefe suffered a dislocated hip , which has been corrected , according to a statement by family spokesman Paul Pastorek . Despite initial reports , there was no serious trauma to O'Keefe 's pelvis , the statement said . The condition of Sean O'Keefe 's son , Kevin , has been upgraded from serious to fair , said Pastorek . `` Despite suffering serious injuries that have required surgery , Kevin is also showing dramatic improvement , '' the statement said . `` Even so , he is very much on the mend . '' Survivor Jim Moorhard remained in fair condition , while William Phillips , whose father died in the crash , remained in good condition , said the Providence Alaska Medical Center . Federal officials are continuing to probe the cause of the crash , said NTSB 's Hersman . They are waiting to speak with the remaining two survivors . Investigators are also working to examine the wreckage of the plane . `` Right now , we 're really in the fact-gathering stage of our investigation , '' said Hersman . CNN 's Paul Vercammen contributed to this report .
NEW : Official says investigators have spoken with two of the survivors . NEW : The pilot was involved in an accident in 1997 . Autopsies show those killed in plane crash suffered blunt force trauma . The condition of the former NASA chief has been upgraded from critical to serious .