Definition
The air pressure inside the induction system of a turbocharged reciprocating engine measured between the turbocharger compressor outlet and the throttle valve. It represents the pressure of the compressed air being delivered to the engine before it is metered by the throttle.
Plain English
The pressure of the air after the turbocharger has squeezed it but before it reaches the throttle. It tells you how hard the turbocharger is working to feed the engine.
Context Anchor
Seen in discussions of turbocharged piston engines, engine power settings, fuel metering, and intake-air troubleshooting.
Derivation
The term comes from the physical layout of the engine: the turbocharger sits 'above' the throttle and intake manifold in the airflow path, so the pressurized air it delivers sits on the 'upper deck' of the induction system, before the throttle drops it down into the manifold.
Why Pilots Care
Maintains safe oxygen levels and prevents discomfort or hypoxia for passengers on the upper deck.
Intuition Check
“Upper deck” does not mean an upper floor or passenger deck of an aircraft here. It means the pressurized intake-air area above, or upstream of, the throttle plate in the engine air system.
Example Sentence 1
The mechanic connected a test gauge to measure upper deck pressure while the engine was run up, to verify the turbocharger was producing the correct boost.
Example Sentence 2
A slight adjustment kept upper deck pressure matched to the lower cabin.