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Our local airport is regularly visited by Cessna caravans flying cargo. This week I saw one parked outside the FBO building that had its exhaust stack bent down to lead under the cowling, where it was connected to a duct suspended from the underside of the fuselage. The duct was perhaps a foot in diameter and ran all the way back to where the tailcone began. Every other Caravan I have ever seen has the exhaust stack exiting the cowling on one side and then terminating. What's up with the ducted exhaust?

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  • $\begingroup$ Caravans or Grand Caravans? Is this particular plane a turboprop, I would imagine so judging by the size of the exhaust? $\endgroup$
    – Jpe61
    Sep 5 at 8:12
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    $\begingroup$ thedrive.com/the-war-zone/14088/… Was it this plane? $\endgroup$
    – MD88Fan
    Sep 5 at 14:35
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    $\begingroup$ That's an answer. It's to clear the exhaust of atmospheric sampling intakes. $\endgroup$
    – John K
    Sep 5 at 17:45
  • $\begingroup$ @md88fan yes yes that's it!!! $\endgroup$ Sep 5 at 17:47
  • $\begingroup$ Holy cow! That’s a lucky catch. Glad I could help. $\endgroup$
    – MD88Fan
    Sep 5 at 19:43
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The aircraft you saw, "ASPECT," is a contractor operated Cessna Grand Caravan used by the EPA to monitor sites of active or possible CBRN disasters.

enter image description here

The reason for the long exhaust stack is simply to keep exhaust gasses from interfering with the sensors on board. As I write this, the aircraft is flying over New Orleans, likely assessing damage from Hurricane Ida:

enter image description here
Source: flightaware.com; Sep 5th, 2021

The mission is similar, though not identical, to the Bell 412s operated by the Dept of State, equipped with sensors to measure radiation- baselines are established for cities and these helicopters can be deployed in the unlikely scenario that radiological material is stolen or a nuclear/radiological weapon is suspected to be nearby. Hope this helps!

Update: per StephenS, this is also common on aerial survey aircraft, but since it has been identified as the ASPECT aircraft, the above remains true.

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    $\begingroup$ Yes it does! this was great. $\endgroup$ Sep 6 at 3:19
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    $\begingroup$ This is also common on aerial survey planes to keep hot, dirty exhaust away from the expensive cameras. $\endgroup$
    – StephenS
    Sep 6 at 16:35

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