AMSTERDAM , Netherlands ( CNN ) -- The nationalities of the people killed in the Turkish Airlines plane crash near Amsterdam 's main airport have been identified as five Turks and four U.S. citizens . Masked investigators work at the crash site Thursday . Among the dead were two Boeing employees , among four onboard the flight , their company said late Thursday in a posting on its Web site . A third was hospitalized , and a fourth employee 's fate was not yet known , the company said . None of their identities have been released . Investigators were trying to determine what caused the crash of the aircraft , a model with a good safety record flown by a well-respected airline at one of the world 's most modern airports . The crash split the plane into three parts , as it was arriving at Schiphol from Istanbul , Turkey , around 10:40 a.m. ( 4:40 a.m . ET ) . Flight 1951 went down in a farmer 's field about 500 yards short of the runway in favorable weather conditions . It had 135 people onboard . Among those injured in the crash , 63 remained hospitalized Thursday , six of them in critical condition , said Theo Weterings , the mayor of Haarlemmermeer municipality , where Amsterdam 's Schiphol Airport is located . Another 25 passengers were severely injured , an official said Tuesday . Authorities have confirmed the nationalities of all but 15 of the passengers and crew , Weterings said . Those on board the flight included 53 Dutch , 51 Turkish , seven Americans , three Britons , and one each from Germany , Bulgaria , Finland , and Taiwan . Watch crash survivors return home » . `` I want to express my deepest sympathies again to the victims of TK flight 1951 , '' Weterings said . One week ago , an employees ' union accused Turkish Airlines of `` inviting disaster '' by ignoring aircraft maintenance , it emerged Thursday . The Turkish Civil Aviation Union alleged on its Web site on February 18 that Turkish Airlines `` is ignoring the most basic function of flight safety , which is plane maintenance services . '' `` The company administration does not understand the consequences of ripping people from their jobs and inviting a disaster . '' The union , which represents 12,000 Turkish Airline employees , is involved in an ugly dispute with the company 's management . Watch how survivors described crash » . Turkish Airlines posted a statement on its Web site on Thursday saying it takes safety seriously and that it followed all `` maintenance procedures of the plane manufacturer , national and international authorities directives '' for the plane . Two days before the crash , the company statement said , the pilot of the plane reported failure with the `` Master Caution Light '' while taxiing . The part was replaced , and `` after this replacement , the plane had eight take-offs and landings and there were no problems , '' Turkish Airlines said . In the wake of the disaster , Turkish Airlines executives and officials from Turkey 's Transportation Ministry said the Boeing 737-800 had last been inspected December 22 . See where 737-800 has been involved in previous incidents » . `` There was no problem with maintenance in the records of the plane , '' Candan Karlicetin , executive board chairman of Turkish Airlines , said in a news conference just hours after the crash . Teams of investigators arrived at the crash site just after daybreak and set up a large white tent . They fanned out over the debris field , where the white fuselage of the Boeing lay in three pieces . A special Turkish Airlines flight landed in Amsterdam Thursday morning from Istanbul , carrying about 70 relatives of those on board the fatal flight . The relatives were accompanied by trauma specialists , the airline said . The flight data and voice recorders were recovered . Turkish officials have also ruled out weather conditions as a possible reason for the crash . Dutch and Turkish authorities say they await the results of an international investigation into the cause . Aviation experts say Turkish Airlines has a relatively good safety record , though in 2003 , more then 70 people were killed when a Turkish Airlines domestic flight crashed in fog near the southeastern city of Diyarbakir . Turkey 's flagship carrier had been expanding its routes and fleet of aircraft in recent years . Hollywood actor Kevin Costner was recently hired to star in an advertising campaign for the company . Costner 's commercials were to be broadcast in 70 countries . An employee in Turkish Airlines ' advertising department said the promotional campaign was suspended in the wake of the fatal plane crash . CNN 's Jim Bittermann in Amsterdam , Netherlands , and Ivan Watson in Istanbul , Turkey , contributed to this report .
Moscow : Two company employees -- among others on flight -- were killed , company says . Moscow : Their bodies have not been released . 63 people remained in the hospital , six in critical condition , mayor says . Plane crashed near Moscow 's main airport , splitting into two parts .