（案例分析）2004年11月21日早上7时45分，内蒙古包头二里半机场（现已经改名包头东河机场），一架隶属于某航云南分公司的庞巴迪CRJ-200型支线客机，准备执飞从包头前往上海虹桥的航班。机上当时一共有3名机组成员、2名空乘、1名安全员和47名乘客。当日包头当地天气处在霜冻期，机场晴空无云，静风天气，能见度3-6公里，天气现象为霾，该机场的停场过程中天气符合结霜条件。而此客机在21号起飞前就在包头机场停场了一夜。该机于起飞后19秒坠毁，机上的53人全部遇难，无一生还，另外还造成2名群众遇难。使得这起一等飞行事故造成的遇难人数达到55人。事故调查过程中，云南公司派驻包头机场放行该次航班的地面人员反映：“2004年11月21日早晨，机务人员对飞机实施例行的外部检查时，用手触摸机翼，发现机翼上有水汽。”但飞机从早晨的例行检查至起飞这两三个小时内没有对飞机再进行过任何外部检查，更没有进行除冰作业。请分析该案例中导致事故发生的原因，作为飞行员你从中得到哪些启示？(Case analysis) On Dec.21, 2004, at 7:45 in Baotou Airport( Donghe airport), a Bombardier CRJ-200 regional jetbelonging to the Yunnan Branch of One Airline was ready to operate Flight from Baotou to Shanghai Hongqiao.There were three crew members, two flight attendants, a security officer and 47 passengers on board.On that day, the local weather in Baotou was in the frost period. The airport was clear and cloudless with calm wind and visibility of 3-6km. The weather phenomenon was haze. the weather in the airport meets the condition for frost accumulation when aircraft parking in this airport. And the aircraft stopped overnight at Baotou Airport just before take-off on 21. The plane crashed 19 seconds after takeoff, killing all 53 people on board and two others, bringing the death toll from the first class air crash to 55.During the investigation of the accident, the ground staff assigned by Yunnan Branch who released the flight at Baotou Airport reported: On the morning of November 21, 2004, when the aircraft was carrying out routine external inspection, the flight crew touched the wing with their hands and found water vapor on the wing."But there were no additional external inspections or deicing operations in the two to three hours from the morning routine inspection to takeoff. Please analyze the causes of the accident in this case. What lessons did you learn as a pilot?