The National Institute for Occupational Safety and Health (NIOSH) received a request for a health hazard evaluation (HHE) from employees at a major airline. The employees were concerned about noise levels they experienced on the ramp area as they serviced inbound and outbound aircraft. Of particular concern was the noise emitted by a regional jet aircraft and its auxiliary power unit (APU) which is located in the tail of the vehicle. The employees felt that the noise from the aircraft was affecting their hearing, leading to permanent damage to their ears. Background: During the evaluation, aircraft were parked in an open area of the airport and passengers were shuttled to and from the planes and terminal in buses. Up to four rows of aircraft were parked in the ramp area. Approximately 100 ramp personnel worked two shifts, servicing the aircraft when the planes were on the ground. Their tasks included baggage handling, aircraft maintenance, lavatory service, and catering. The aircraft taxi to their parking locations with the engines operating. Once parked, the pilot will turn off the engine, which stops the on-board ventilation system. In order to keep the air in the cabin cooled or heated, either the APU or ground power unit (GPU) and air conditioning (A/C) cart will be placed in service. The APU is an on-board engine that supplies power to the aircraft and the ventilation system, and is most often located in the tail of the aircraft. On the regional jet, the APU is exhausted down toward the ground through the end of the plane's tail section. The door for the baggage compartment is located adjacent to the tail section on the port side of the aircraft. The noise created by the APU was specified in the HHE request as the cause for employees' concerns. Personal noise dosimeter measurements were taken of customer service agents during a full shift workday to evaluate the noise impact from the APU. Area spectral measurements were also taken at fixed locations around the aircraft. The company's hearing conservation program was reviewed with particular attention given to the kinds of hearing protection offered to the employees. Conclusions: Ramp employees are exposed to noise levels that could be potentially damaging to their hearing. In most instances, the HPDs that the company provides are effective in reducing the exposures to levels that do not increase their risk of occupational hearing loss. However, because of the exposure levels, the airline should continue to provide their employees all of the components of a hearing loss prevention program, including noise monitoring, audiometric testing, HPDs, and recordkeeping. The company should continue to pursue ways to control noise exposures to the ramp employees through changes in work practices, facility redesign, and retro. t controls for the aircraft.