Another U.S. government agency decided to ditch Research in Motion's (RIM) beleaguered BlackBerry because the smartphone is not reliable enough.

In yet another blow to the already struggling RIM, the U.S. National Transportation Safety Board (NTSB) has decided to drop BlackBerry in favor of Apple's latest smartphone, the iPhone 5. NTSB joins a growing number of government agencies that have ditched RIM's BlackBerry for more reliable and popular platforms.

According to Bloomberg, NTSB announced its plan to ditch BlackBerry in a government filing last week, explaining that RIM's smartphone is not reliable.

"This requirement is for the acquisition of Apple iPhone 5 devices. These Apple devices will replace the NTSB's existing BlackBerry devices, which have been failing both at inopportune times and at an unacceptable rate. The NTSB requires effective, reliable and stable communication capabilities to carry out its primary investigative mission and to ensure employee safety in remote locations," wrote the agency.

The NTSB is charged with immediately investigating airplane accidents and other transportation disasters. RIM's BlackBerry network has had two international service disruptions, one of which occurred in September, adding up to the NTSB's dissatisfaction with the service. The agency will now be shifting its 400 employees to the iPhone 5 instead of BlackBerry.

RIM has been struggling this year to keep its BlackBerry device relevant in an increasingly competitive environment, and things haven't been easy for the beleaguered company. The U.S. Immigration and Customs Enforcement agency has decided last month to ditch BlackBerry as well, arguing that the smartphone is no longer capable of meeting the mobile technology needs of the agency.

Moreover, the U.S. Department of Defense also announced last month that it was pulling out of its exclusive contract with RIM and opening up bidding to other device makers, including market leaders Apple and Google.

Though government agencies seem to be ditching BlackBerry one by one, RIM remains positive that it will still be able to keep its head above the water.

"Government organizations globally have trusted the reliability and security of BlackBerry for over a decade. They can continue to do so," a spokesperson for RIM told CNET in an emailed statement. "We have 1 million government customers in North America alone who depend on BlackBerry, and more than 400,000 government customers worldwide upgraded their devices in the past year."

The beleaguered company is relying on the upcoming BlackBerry 10 to revive its struggling business. After several delays, BlackBerry 10 is set to launch on Jan.30 with an upgraded operating system and a radical change in design: a full touch-screen.

RIM has also won key government certification for BlackBerry 10, which means the smartphone can be used in secure government workplaces. The company pledged to continue serving government agencies as BlackBerry 10 customers.

"We are committed to the mobility needs of government agencies around the world and will continue to meet these needs with BlackBerry 10," added the company spokesperson.