Possible Clues:

• Racks etc horse goes over given several attempts
• Framework of steel bars on side supports, for film cameras perhaps
• Launch pad sights
• Gear isn't wobbly in engineered frameworks
• Supports attempts to back horse to come first
• 'Overhead structures for equipment, cameras say (8)'
• Bridges for travelling cranes
• Spanning frameworks
• Angriest (anag.)