All certificated pilots, with the exception of those with a sport or Recreational pilot certificate (or when in command of balloons or gliders, including power assisted gliders), are required to maintain a medical certification commensurate with the privileges they intend to exercise as pilot-in-command of an aircraft. For sport pilot certificate applicants or holders, regulations state that a medical is required if the applicant/pilot does not hold a valid United States drivers license. To obtain a medical certification, pilots are required to undergo a medical examination from an Aviation Medical Examiner, or AME. The Aviation Medical Examiner performs an examination based upon the class of certification desired. Medical certifications are divided into three classes:  Third class certifications require the least involved examinations of all medical certifications. They are required for those intending to be pilot-in-command of an aircraft under the Private or Recreational pilot certificates or while exercising solo privileges as a student pilot. To qualify for a third class medical certificate, pilots must meet the following requirements:  For pilots under 40 years of age, third class medical certificates expire on the last day of the month they were issued, five years from the date of issue. The FAA changed this rule from three to five years on July 24, 2008. For all others, they expire on the last day of the month they were issued, two years from the date of issue. In December 2015, the U.S. Senate passed a bill sponsored by Montana Senator Steve Daines, S. 571- Pilot's Bill of Rights 2 (PBOR 2). If signed into law, the bill would expand the third class medical exemption for recreational pilots by reforming the FAA's medical certification process to include more qualified, trained pilots. A second class medical is required for those intending to exercise the privileges of the commercial pilot certificate. It is possible to obtain a commercial pilot certificate while holding a third class medical, but with the exception of flight instruction, the licensee cannot exercise privileges beyond that of a private pilot. To qualify for a second class medical certificate, pilots must meet the requirements for the third class certificate plus:  Second class certificates are valid until the last day of the month, twelve months after they were issued. The certificate holder may then only exercise the privileges of a third class medical certificate. First class certificates are required for those intending to be pilot-in-command in an air carrier operation requiring an Airline Transport Pilot (ATP) certificate. Other operations, including those under Part 91, may require a first class medical for insurance purposes, although it is not a federal requirement in such cases.