When a Dana Air plane crashed in Lagos, Nigeria on Sunday, it aroused concerns that, despite improvements made over the last five years, there are still major safety issues in the West African nation's aviation industry.

Nigerian air safety authorities have confirmed that at least 153 people perished when the plane crashed into a residential building in Ishaga, a neighborhood near Murtala Muhammed Airport. The McDonnell Douglas MD-83 was on its way from the capital Abuja when it crashed into the two-story building Sunday, killing all on board. The number of casualties on the ground remains unclear, but state-owned Radio Nigeria puts the number at 10.

At about 3:43 p.m. local time, Dana Flight 0992 from Abuja to Lagos declared an emergency, a call for May Day to the Lagos control tower, from about 11 nautical miles, Aviation Minister Stella Oduah told state-owned NTA television on Monday. A minute later the aircraft disappeared from the air traffic control radar.

The tragedy was Nigeria's fourth major crash in the past decade and the worst since Jan. 22, 1973 when a passenger plane carrying 176 passengers and crew went down in the northern provincial capital of Kano.

After a spate of cashes in 2005, Nigeria made improving its aviation safety record a priority. President Goodluck Jonathan echoed that sentiment on Sunday.

A spokesman for the president said that every possible effort will be made to ensure that the right lessons are learnt ... and that further measures will be put in place to boost aviation safety in the country.

The president joins all Nigerians in mourning all those who lost their lives in the plane crash which has sadly plunged the nation into ... sorrow, a representative of President Jonathan's office said, according to Reuters.

Dana Air canceled all flights on Monday while President Jonathan declared three days of national mourning, pledging the fullest possible investigation into the crash.

Since 2005, the government has instituted a number of reforms to its air safety systems, introducing modern passenger-scanning equipment and improving its airport radar systems. The improvements earned the nation the Federal Aviation Administration's highest rating, a Category 1, allowing Nigeria's commercial carriers to land at U.S. airports beginning in 2010.

While the reforms may look good on paper, the implementation has been spotty at best. Sporadic power outages in Nigeria, Africa's second-biggest economy, often close air traffic control systems for hours, delaying takeoffs and arrivals and making radar screens go blank. Moreover, the age of the nation's fleet has come into question.

Indian-owned Dana Air, based out of Lagos' Murtala Muhammed Airport, has grown to become one of the oil-rich nation's leading airlines since its inaugural flight from Lagos to Abuja in November 2008, operating over 18 daily domestic flights to Abuja, Calabar, Lagos, Port Harcourt, and Uyo. According to the airline's website, it was named Best Safety and Security Conscious Airline in Nigeria at the Security Watch Africa Awards in September 2010.

While Dana Air may be considered one of the safer and more efficient domestic airlines, the average age of its fleet is 21.4 years and its youngest plane is 20.9 years old, according to Planespotters.net. By comparison, the U.S. domestic fleet averages around 13 years.

According to a Nigerian aviation blog, the plane that crashed on Sunday was a former Alaska Airlines MD-83 built in 1990. On May 11, a similar Dana Air plane -- or possibly the same one -- developed a technical problem and was forced to make an emergency landing in Lagos, the BBC reported.

Many commercial airlines in Nigeria and throughout the region purchase older vessels after they've been retired from fleets in richer countries. The safety of these older planes depends on how rigorously the ground crew maintains them.

The two major crashes in 2005 highlight this concern. The Lagos-based Bellview Airlines Flight 210, a Boeing 737-200, was 24 years old when it crashed on Oct. 22, 2005. The Sosoliso Flight 1145, a McDonnell Douglas DC-9, was 32 years old when it crashed on Dec. 10, 2005.

Africa has the world's lowest air traffic rate with only 3 percent of the population traveling by plane. Despite this, the continent has the highest airline accident rate, accounting for 17 percent of global cases, based on statistics from Montreal-based International Civil Aviation Organization.

Lagos has a population of around 15 million and its international airport is a major hub for the region.  According to the most recent statistics provided by the Federal Airports Authority of Nigeria, Lagos serves over 2.3 million passengers each year.