Diesel Law Exam No. 4 Questions taken from the Pennsylvania Bituminous Mine Officials Exam Study Guide Progress Indicator: Question 1 of 15 1.  Schedule of maintenance. -- At intervals ________________ engine operation, a qualified mechanic shall perform the following maintenance and make all necessary adjustments or repairs or remove the equipment from service: [416] Choices: of one hundred hours of underground not exceeding one hundred hours of within two hundred hours of not exceeding one hundred hours of underground