Descent - Rich or Lean

I recently was flying with another Cirrus pilot, and upon descending I fully enrichened the mixture. He suggested that I was wasting gas, and possibly fouling my plugs, which made sense to me.

The POH says to use full rich on descent. Any thoughts on this?

SR20 or SR22? The former has an altitude-compensating fuel pump, the latter does not.

In the 22 I’ve gotten reasonably good at knowing roughly where the max-power mixture setting is for various altitudes (given that most of the airports I fly to are above 5000 feet) and in descent I enrich the mixture more or less the same way (and these settings are quite rich of peak.) Ultimately it boils down to two things–will the engine quit in descent (unlikely) and will the mixture be where you want it to be, more or less, if you have to do a full-power go-around? For the SR20, just shove it full forward. For the SR22, my habit seems to work reasonably well.

Mine is an SR20. Thanks for your input.


Are you reducing your power on descents or maintaining cruise power. If you are at 65% or below, it probably does not make that much difference. If the engine starts ot run rough, richen it until it stops, and maybe a little more.

According to Deakin (Pelican Perch on AVWeb) there is no need to rush richening the mixtrue on descent, and if you are at 65% or less power setting, then you will not hurt the engine either way. Too rich or too lean you can cause theengine to quit, but correcting the mixture will (should) cause it to resatrt spontaneously.

A big plus for the ARNAV EngineView is that is shows the % power.


>A big plus for the ARNAV EngineView is that is shows the % power.

Sort of.

It shows the power you WOULD have if you were operating full rich. It does not sense (and compensate for) the effect of leaning.

If I set my SR20 to 80% power (indicated by ARNAV EngineView), and then lean to 50 degrees LOP as advocated by Deakin, my airspeed indicator and my Garmins let me know in no uncertain terms that I have MUCH LESS power available to me; but EngineView continues showing 80%. I really wish they’d use the fuel-flow, and infer the power from that – theoretically, it can be done accurately, because fuel-flow is a pretty direct indicator of power being developed, as long as none is leaking!

  • Mike.