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maximum altitude loss

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Aerodynamics, Aircraft Systems

Hello, 

I'm wondering if there is a maximum altitude loss safe to an engine while practicing an emergency decent? say I start at 6500 and begin an e-dec down to 2500. power off, mixture rich, carb heat out.  I am banking 30 degrees and holding 120 ias in a Cessna 172m. Also, is is ok to transition back and forth from left to right banks while holding airspeed? I dropped from 5500 to 1500 this evening while flying from Long Beach To Montgomery field, just south of Camp Pendleton, off shore. when I leveled off, the engine seemed to be louder and vibrating a bit more than it was pre-decent. it also caused engine noise through my headphones, with active noise canceling on. The Engine didn't seem to be making this noise when I took them off. temps, pressure, and suction were all good. made it home fine, but with my feet vibrating a bit more than usual. 

 

Ben

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1 Answers



  1. Boston Air on Apr 29, 2020

    There are several engine related items to be concerned with during practice emergency descents.

    1. Shock cooling – due to the extended high airspeed descent with power at idle, the engine will rapidly cool. However, this is of greater concern with the more powerful (and hotter running engines) such as the IO-540, etc. Those types of engines are equipped with pilot controllable cowl flaps to better manage engine temperatures. The smaller engine in your Cessna 172 wouldn’t be as susceptible. I would just limit the amount of times you practice this maneuver on a given flight. You can also “clear the engine” occasionally during the descent by briefly adding power. At the school where I teach, we add power then retard to idle every 1,000′ during prolonged power off descents such as simulated engine failures and emergency descents. This will help warm the engine and verify it’s operation.

    2. Carb ice – due to the rapid cooling of the engine during an emergency descent, the engine could be susceptible to developing carb ice. As long as you apply carb heat during your pre-maneuver setup (which it sounds like you did) this would be a minimal concern. If you thought the engine was running slightly rough after completing the maneuver, you should leave the carb heat on for a few minutes and determine if the situation improves.

    3. Fuel delivery – due to the high bank angle in an emergency descent coupled with a high pitch down angle, ensure you follow the manufacturer’s recommendation for using the fuel pump(s) and the correct fuel selector setting. Failing to do so could result in fuel starvation issues.

    Sounds like you did the right thing by returning to the airport when you detected a possible engine issue. Never hurts to play it safe and get the aircraft checked out by a mechanic. Fly safe and keep training.

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