Final answer:
Do not use the head-tilt/chin-lift technique for opening a casualty's airway if a spinal injury is suspected; instead, use the jaw-thrust technique while keeping the head and neck still, or let trained professionals manage the airway in such cases.
Step-by-step explanation:
When opening a casualty's airway, one should not use the head-tilt/chin-lift technique if a spinal injury is suspected. Introducing any movement to the cervical spine could cause further injury. Since maintaining spinal alignment is crucial, the preferred method is the jaw-thrust technique, which can be performed without moving the head or neck. However, if you're not trained or confident in applying the jaw-thrust technique, it is advised to leave the airway management to the professionals, especially in cases of suspected spinal injury.