Nigerian plane reported engine trouble before crashing Sunday The toll in Sunday's plane crash in Nigeria, which killed all 153 on board, may be scores higher once fatalities on the ground are established, according to Nigerian media reports. Officials of the Nigerian Civil Aviation Authority said the pilot reported engine trouble shortly before Flight NJ992 went down as it was nearing the airport in Lagos, the country's commercial capital, according to local media reports. The number of people on the ground killed when the Dana Air Boeing MD-83 crashed in a crowded residential neighborhood is not clear. President Goodluck Jonathan visited the scene Monday after declaring three days of mourning and ordering an investigation. Nigerian flags flew at half staff Monday. The aircraft lost altitude rapidly and plowed into a residential building and a printing works before bursting into flames. "The fear is that since it happened in a residential area, there may have been many people killed," Yushau Shuaib, a spokesman for Nigeria's National Emergency Management Agency, told the Associated Press. The flight recorder has been recovered, according to The Nation newspaper, citing an official from the National Emergency Management Agency. Its recovery should help determine what brought down the plane. Dana Air has been operating in Nigeria since 2008. The airline carried a condolence message on its website Monday -- "May the souls of the deceased rest in peace" -- along with numbers for a 24-hour call center. The civil aviation authority website carried photos of the burning wreck and a link to the passenger manifest. The Dana Air plane was en route from Abuja, the capital, along one of the country's most important air routes. Several army generals and many members of Nigeria's political elite and civil society were killed, according to local media reports. There were some foreigners on board, including six Chinese, according to the New China News Agency. The passenger list was released through leaks published on Twitter before authorities released the names. Thousands flocked to the scene of the crash and police at one point fired tear gas to control the crowd. It is the fourth crash in less than seven years involving a Nigerian domestic carrier in which more than 100 people died. A Bellview Airlines flight crashed in October 2005 killing all 177 on board. In December 2005, a Sosoliso Airlines flight crashed killing 103, including many schoolchildren. In October 2006, an ADC Airlines plane crashed, killing 106 of the 114 on board. However, Nigeria's air safety appeared to improve in recent years. In 2010, the U.S. Federal Aviation Authority announced a category 1 safety rating, meaning the country complied with international safety standards in relation to training, technical expertise and other issues. Dana Airlines Chief Executive Jacky Hathiramani issued a statement Monday saying the airline was saddened by the loss of the passengers and crew on the flight. Hathiramani said Dana was cooperating with Nigerian investigators and officials from the U.S. National Transportation Safety Board who were assisting in the investigation. At the site of the crash Monday, Jonathan vowed improvements in Nigerian air safety. We have been working very hard to improve the aviation in this country. This particular incident is a major setback for us. By the end of the day, I will make sure that this will not repeat itself in the country," Jonathan told reporters at the scene. Jonathan's press spokesman, Reuben Abati, was criticized Monday for tweeting from the crash scene: "A president that cares. Going to the site of plane crash in Lagos.