U.S. official : `` We need to maintain respectful optimism and be responsible '' Expert says refined search area manageable for underwater vessels . Possible discovery of plane 's pingers energizes search , but for how much longer ? Agency : Up to 15 planes are searching the ocean floor in a coordinated effort that could take months or years.
U.S. official : `` We need to maintain respectful optimism and be responsible '' Expert says refined search area manageable for underwater vessels . Possible discovery of plane 's pingers energizes search , but for how much longer ? Agency : Up to 15 planes , 14 ships could take part in Wednesday 's search .