Passive noise reduction is the sound reduction achieved by cupping hands over the ears, or by inserting earplugs into the ears. PNR is somewhat effective at blocking mid and high frequency sound, but does not block low frequency sound. Unfortunately, mid and high frequency sound includes the ranges of human speech, as well as the warning sounds used to alert of fire, low altitude, and configuration problems in jet airliners. This means that PNR is somewhat effective in reducing sounds that airline pilots want to hear clearly. In jet airline aircraft, low frequency noise is caused by wind, engine vibration, air-conditioning systems, hydraulic pumps, and other aircraft systems. PNR is ineffective at reducing sounds that airline pilots flying jets most want reduced.

PNR headsets feature large ear cups designed to completely enclose the ear. Ear seal quality is important in these headsets, and both the age of the headset and other factors such as wearing glasses under the headset will reduce effectiveness. PNR headsets make it difficult to hear other crew members unless an intercom is used. Many airline pilots do not use intercoms for in cockpit communication. PNR headsets would not be a good choice for pilots because of their limited effectiveness in reducing the type of noise experienced in jet airline aircraft.