The TOT Spike That Wasn't Logged and What It Cost Six Months Later
Every rotorcraft operator knows the cycle. The aircraft is in the hangar for a scheduled inspection and the engineer finds a turbine outlet temperature exceedance recorded in the FADEC data that nobody logged in the paper system. The pilot doesn't remember — it might have been a hot start, might have been a sustained high-power demand on a hot day at altitude. Without a concurrent log entry showing the OAT, altitude, torque, and N1 at the time of the event, the engineer has FADEC data but no operational context to determine whether the exceedance was a transient or a sustained over-temperature condition that requires a hot-section inspection.
Logged. Everything. Every flight.
Hobbs Time: The Clock That Bills and Schedules
Hobbs Start and Hobbs Stop feed the Hobbs Time calculation — the direct airframe utilisation measure that drives scheduled maintenance intervals. At 100 hours, oil change and inspection. At 300 hours, rotor head inspection. At 2200 hours, engine hot section. If the Hobbs entries are inconsistent, unreliable, or missing, the entire maintenance programme drifts.
Logbook Time is the calculated FAA/CAA loggable flight time, which may differ from Hobbs time depending on the aircraft's meter configuration. Landings is an integer count; Lift Offs is calculated as Landings plus any touch-and-go cycles. Both drive airframe cycle counts for components with life-limited certification.
Engine Parameters: Seven Numbers That Describe What the Engine Was Doing
OAT (Outside Air Temperature), TOT (Turbine Outlet Temperature), Torque, N1. Four thermodynamic and performance parameters that together tell you whether the engine was operating within its approved envelope for the flight conditions.
TOT without OAT is meaningless — a TOT of 765°C on a cold ISA day at sea level is very different from the same reading at 8,000 feet on a 35°C day. The combination of OAT, altitude, and TOT gives you the temperature margin above the approved limit for the conditions. When that margin is consistently narrowing over successive log entries on the same aircraft, you have early warning of a deteriorating hot-section before the FADEC triggers an exceedance alert.
Engine Oil Temperature, Engine Oil Pressure, Transmission Oil Temperature, Transmission Oil Pressure. Four more parameters. Oil pressure below the lower limit during cruise is an emergency. Oil temperature trending toward the upper limit over successive flights on the same aircraft without explanation is a finding that goes to maintenance before it becomes an emergency.
Fuel Flow quantifies consumption. On a turbine engine with a metered fuel system, fuel flow at a given torque and N1 setting should be predictable within tight tolerances. Drift in that relationship is an early indicator of fuel control unit degradation.
PFR Number links the log entry to a Post Flight Report if one was raised. NAC Flight flags Night Air Carrier operations — a regulatory classification that changes rest requirements, crew currency requirements, and the applicable operating rules for the flight. One field, one boolean, and the compliance record is built automatically as you log.