BROOKLYN - The Metropolitan Transportation Authority (MTA) is launching online alerts for residents in Brooklyn and the rest of the city who use its elevators and escalators.The move is the first step in a plan to keep riders from being delayed or inconvenienced due to broken equipment. Previously, riders were only able to call a hotline that was updated four times a day. The online alerts will be updated three times a day, but the MTA says it plans to provide around-the-clock e-mail and Web site updates starting in the fall.Advocates for disabled riders are praising the change, but say the MTA still needs to do a better job repairing elevators and escalators that aren't working.There are 158 elevators and 169 escalators at subway stations across the city.