Tracheal tube cuff pressures increased from a mean 28.7 cm H₂O pre-flight to 62.6 cm H₂O in flight (mean altitude increase 2260 feet) in a Swiss helicopter-based study.
At cruising altitude, 98% of patients had intracuff pressure >30 cm H₂O, 72% had intracuff pressure>50 cm H₂O, and 20% even had intracuff pressure>80 cm H₂O.
Multiple different referring hospitals meant the type of tracheal tube was not controlled for.

Endotracheal Tube Intracuff Pressure During Helicopter Transport
Ann Emerg Med. 2010 Aug;56(2):89-93