French air safety investigators said Wednesday that they might never find the data recorders from the Air France jetliner that crashed in the Atlantic Ocean this week. The plane's 'black box' digital data and cockpit voice recorders have so-called underwater locator beacons, or pingers, that activate when the boxes get wet and typically generate signals for about 30 days. Investigators view information recovered from the recorders as a key tool in understanding crashes. But French investigators said it would be difficult to find the boxes, describing the area where they sank as 'deep and mountainous,' Agence France-Presse reported. Furthermore, recovery crews will have to battle heavy thunderstorms and rough seas, according to Accuweather.com. Sound quality from the pingers can be degraded by water temperature and underwater terrain. The signal will be especially hard to pick up if the devices, for example, are stuck in a canyon on the ocean floor. Aviation safety experts, however, say investigators generally have had success locating black boxes, even in deep waters. Accuweather.com meteorologists said debris from the plane was found in an area of the Atlantic Ocean with depths of 9,000 feet. The black boxes on the Airbus A330 can transmit signals from depths of 14,000 feet to 15,000 feet. William Voss, president of the Flight Safety Foundation, said he believed that French air officials were downplaying their chances of locating the black boxes as a way to manage expectations of the investigation with the French public. 'They will resurrect Jacques Cousteau if they have to -- they want them bad,' he said. The boxes 'are trying to be found,' Voss said. 'The navies involved have sophisticated equipment designed to find submarines that are trying to hide. I think there is a good possibility that they will be able to locate these boxes.' The cockpit recorder records radio transmissions and ambient sounds in the cockpit, such as pilots' voices and engine noise. Data recorders monitor altitude, time, speed and other flight parameters. Air France flight 447, on an overnight flight from Rio de Janeiro to Paris, was last heard from Monday when automatic emergency signals beginning at 4:14 a.m. Paris time indicated that all its systems had failed, according to Air France and French officials. There was no mayday signal and no communication from the pilot, indicating that there was probably a sudden catastrophe, the airline has said. Those aboard the flight included 61 French citizens, 58 Brazilians and nationals from 29 other countries, including two Americans, according to a list compiled by Air France. A memorial was held in Paris at Notre Dame Cathedral for the families of those killed. President Nicolas Sarkozy attended the service. 