all. Sec. 545. Prioritizing accountability and accessibility for aviation consumers. Sec. 546. Accommodations for qualified individuals with disabilities. Sec. 547. Equal accessibility to passenger portals. Sec. 548. Aircraft access standards. Sec. 549. Investigation of complaints. Sec. 550. Removal of outdated references to passengers with disabilities. Sec. 551. On-board wheelchairs in aircraft cabin. Sec. 552. Aircraft accessibility. Subtitle C—Air Service Development Sec. 561. Essential air service reforms. Sec. 562. Small community air service development grants. Sec. 563. GAO study and report on the alternate essential air service pilot program. Sec. 564. Essential air service in parts of Alaska. Sec. 565. Essential air service community petition for review. Sec. 566. Essential air service authorization. Sec. 567. GAO study on costs of essential air service. Sec. 568. Response time for applications to provide essential air service. Sec. 569. GAO study on certain airport delays. Sec. 570. Report on restoration of small community air service. TITLE VI—Modernizing the National Airspace System Sec. 601. Instrument landing system installation. Sec. 602. Navigation aids study. Sec. 603. NextGen accountability review. Sec. 604. Airspace access. Sec. 605. FAA contract tower workforce audit. Sec. 606. Air traffic control tower safety. Sec. 607. Air traffic services data reports. Sec. 608. Consideration of small hub control towers. Sec. 609. Flight profile optimization. Sec. 610. Extension of enhanced air traffic services pilot program. Sec. 611. Federal contact tower wage determinations and positions. Sec. 612. Briefing on radio communications coverage around mountainous terrain. Sec. 613. Aeronautical mobile communications services. Sec. 614. Delivery of clearance to pilots via internet protocol. Sec. 615. Study on congested airspace. Sec. 616. Briefing on LIT VORTAC project. Sec. 617. Surface surveillance. Sec. 618. Consideration of third-party services. Sec. 619. NextGen programs. Sec. 620. Contract Tower