Air-to-air refueling (AAR) is the process of transferring fuel from one aircraft to another while both are in flight Air to Air Refuelling. In-flight refuelling is a technique that allows fuel to be transferred from one aircraft, called a tanker, to another while both are mid-air. This allows the receiving aircraft to stay airborne longer and take off with a greater payload. It is used for military purposes and no civilian applications are known.

• A specially equipped aircraft, called the tanker, carries fuel to another aircraft, called the receiver. 
• The tanker positions itself in front of the receiver
• A hose is dropped from the tanker to the receiver. 
• The receiver aircraft receives fuel through the hose
• An Air Refueling Officer (ARO) monitors the process and controls the fuel volume and refueling speed. 

• Increased range: Aircraft can fly farther without landing to refuel. 

• Reduced fuel consumption: Aircraft can fly at more efficient altitudes and reduce the need to land and take off. 
• Improved safety: Aircraft are less likely to crash due to fuel exhaustion
• Increased flexibility: Aircraft can change flight plans or respond to emergencies without landing. 
• Increased efficiency: Aircraft can complete missions faster and respond to emergencies more effectively.
• Increased payload: Aircraft can carry more weapons, cargo, or personnel. 

• High pilot skill needed:
  Precise maneuvering is required to connect with the refueling boom or drogue, necessitating extensive training for both tanker and receiver pilots. 
• Weather dependence:
  Turbulence and poor visibility can significantly complicate refueling operations. 
• Vulnerability during refueling:
  Aircraft are most vulnerable to attack when closely coupled to a tanker, limiting their defensive capabilities. 
• Compatibility issues:
  Different aircraft may use incompatible refueling systems (boom vs. drogue), limiting interoperability between different air forces. 

• Autonomous Assets Air-to-Air Refueling (A4R): Airbus’s AutoMate campaign tested a technology demonstrator for A4R, which would automate the entire refueling process. 
• Automatic air-to-air refueling (A3R): Airbus’s A3R system uses automation to align the boom tip with the receiving aircraft’s intake. 
• Unmanned tankers: The MQ-25 will be the first unmanned tanker into production.