10.5 Exhaust Systems, Thrust Reversers, and Temperature Patterns

Hot Gas, Structure, and Directional Control

Exhaust systems remove combustion gases after useful energy has been extracted. In reciprocating engines, exhaust stacks, mufflers, heat exchangers, turbocharger turbines, and tailpipes must contain hot gas and protect the cabin from carbon monoxide. In turbine engines, exhaust ducts, nozzles, tailcones, mixers, and reversers influence thrust, temperature distribution, noise, and structure. The Powerplant ACS expects mechanics to understand both normal function and the consequences of cracks, leakage, restriction, and faulty reverser operation.

Reciprocating exhaust leaks are not minor cosmetic defects. Hot gas can cut metal, burn hoses, damage wiring, and ignite nearby fluid. If the exhaust system supplies cabin heat through a shroud, a crack can allow carbon monoxide into the cabin air path. That is why muffler and heat exchanger inspections matter. A soot trail, burned area, unusual smell, or carbon monoxide complaint must be treated as evidence of leakage until inspection proves otherwise.

Turbocharged reciprocating engines add another exhaust cause. The turbine depends on exhaust energy. A leak upstream of the turbine reduces the energy available to spin the turbocharger, causing low manifold pressure or slow boost response. The same leak can overheat surrounding components. A leak downstream of the turbine may be less likely to reduce boost but can still create heat and structural hazards. Location controls the symptom.

Turbine exhaust systems affect thrust and temperature patterns. A damaged nozzle, tailpipe, mixer, or thrust reverser blocker door can disturb flow and reduce efficiency. Rising exhaust gas temperature for the same power may indicate engine deterioration, but exhaust path damage can contribute. Cracks may grow from thermal cycling and vibration. Discoloration, distortion, missing hardware, and rub marks are practical clues. A mechanic should connect visible damage to gas-path leakage, vibration, and performance trends.

Thrust reversers redirect thrust for landing deceleration after touchdown according to aircraft design. They may use blocker doors, translating sleeves, cascade vanes, buckets, hydraulic power, pneumatic power, electrical control, and mechanical locks. The dangerous faults are unintended deployment, failure to deploy, failure to stow, unlocked indications, and asymmetric operation. Maintenance troubleshooting must verify lock integrity, actuator travel, proximity switches, hydraulic or pneumatic leaks, rigging, and cockpit indications.

Use this exhaust and reverser checklist:

1. Look for soot, burned structure, cracks, missing clamps, loose hardware, distortion, and heat-shield damage.
2. For reciprocating heat exchangers, consider carbon monoxide risk whenever cracks or heater complaints appear.
3. For turbocharged engines, locate leaks before or after the turbine to predict boost effects.
4. For turbine engines, compare EGT trend, thrust response, vibration, and visual damage.
5. For reversers, verify commanded position, actual position, lock status, symmetry, and indication agreement.

For exam questions, the most important word is often location. An exhaust leak before a turbocharger turbine changes boost. A leak inside a heater shroud changes cabin safety. A reverser that indicates unlocked changes dispatch and ground safety. A crack in a hot section changes inspection urgency because heat and vibration make small defects grow.