Verify - Request confirmation of information. Wilco - I have received your message, understand it, and will comply. Because some letters sound similar, the following words are used to reduce confusion. For example, taxiway B would be referred to as taxiway Bravo. L Lima Y Yankee M Mike Z Zulu Light Signals Air traffic controllers have a backup system for communicating with pilots if the aircraft's or controller's radios fail.
Controllers use a light gun with different colors to tell pilots or vehicle drivers what to do.
If you are ever working on a runway or taxiway and your radio quits, you should turn your vehicle towards the tower, start flashing your headlights and the controller will signal you with the light gun. This may take some time if the controller's attention is directed towards another part of the airport. Even a failed radio is not an excuse for proceeding without a proper clearance.