Multi engine slow flight speed

Arob16

Arob16

Pre-takeoff checklist
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Arob16
I posted this question on another forum but interested in other opinions as well...

I wanted to get opinions on the commercial-multi slow flight speed required to perform the slow flight maneuver. Our school's Baron B55 manuevers checklist states that slow flight should be accomplished at 88-90 KIAS (+10 kts higher than Vmc, +20 kts higher than stall speed). I always thought this was due to risk of engine failure below Vmc, if flying closer to where slow flight "should" be flown (i.e. +5-10 kts above stall speed). Stall speed in the Baron is 68 kts, Vmc is 78 kts. Instructors at my flight school differ on this, the ACS requires a speed where "any further increase in angle of attack, increase in load factor, or reduction in power, would result in a stall warning". The B55 POH does not specify a slow flight speed. But I completely understand why you would want to maneuver in slow flight above Vmc.

So what does everyone else teach? Slow flight below Vmc, or above Vmc for safety?
 
I was taught right at the horn, although now it would be right above the horn. Too bad you have differing opinions; if only there was some kind of standard we could follow.
 
It's been a long time since I've flown a B55 so I can't give you a specific speed. But like dmspilot suggested, I'd do it right above where the stall warner comes on.

As far as Vmc vs. slow flight goes, give a little thought to the factors of Vmc that you've likely discussed with your instructor. Is the published Vmc number representative of how you're flying the airplane in slow flight? Why or why not? Would you be more or less at risk of a loss of control in the event of an engine failure?
 
Slow flight above Vmc hardly teaches anything. Be "just at or above the stall" per the ACS. I hope you're not holding blueline to the numbers either. That was something I was taught at ATP that I had to unlearn. :D

Note that the speed at which you'll be demonstrating slow flight will be BELOW Vsse (or at least it is in my Baron), so make sure your MEI isn't chopping engines on you intentionally. Brief beforehand unless you like unrecoverable spins.

If you dig (or search the PDF) in the manual, you can find a very large-font prohibition against intentional engine cuts below Vsse. This should supercede anyone else's argument to do engine cuts slower, including the DPE's if it comes to that.
 
If you lose an engine while below Vmc immediately bring back the power on the good engine and lower the nose to increase airspeed. If you are not developing power below Vmc there is no chance of it becoming an unrecoverable spin.
 
Thanks for the feedback all... I agree, slow flight is a maneuver just above stall speed, not sure why our maneuver checklist states the higher speed. At 90 kts the thing wants to continue climbing anyway.
 
Why should there be any differing opinions? The Airman Certification Standards spells it out.

CA.VII.A.S1 Clear the area.
CA.VII.A.S2 Select an entry altitude that will allow the Task to be completed no lower than 1,500 feet AGL (ASEL, ASES) or 3,000 feet AGL (AMEL, AMES).
CA.VII.A.S3 Establish and maintain an airspeed at which any further increase in angle of attack, increase in load factor, or reduction in power, would result in a stall warning (e.g., airplane buffet, stall horn, etc.).
CA.VII.A.S4 Accomplish coordinated straight-and-level flight, turns, climbs, and descents with the aircraft configured as specified by the evaluator without a stall warning (e.g., airplane buffet, stall horn, etc.).
CA.VII.A.S5 Maintain the specified altitude, ±50 feet; specified heading, ±10°; airspeed, +5/-0 knots; and specified angle of bank, ±5°.

There's a significant difference between "just above stall speed" and what is specified in S3.

A little additional insight from the Airplane Flying Handbook, FAA-H-8083-3B, Chapter 4...

"Slow flight is when the airplane AOA is just under the AOA which will cause an aerodynamic buffet or a warning from a stall warning device if equipped with one."​

... and...

"For pilot training and testing purposes, slow flight includes two main elements:

1. Slowing to, maneuvering at, and recovering from an airspeed at which the airplane is still capable of maintaining controlled flight without activating the stall warning—5 to 10 knots above the 1G stall speed is a good target; and
2. Performing slow flight in configurations appropriate to takeoffs, climbs, descents, approaches to landing, and go-arounds."​

By the way, 68 knots * 1.3 = 88.4 knots. Vref is usually Vso * 1.3. A basic Vref style speed could be what they're after "for safety," but that would not be a satisfactory airspeed selection for the purpose of demonstrating slow flight on the practical test.
 
schmookeeg said:
Slow flight above Vmc hardly teaches anything. Be "just at or above the stall" per the ACS. I hope you're not holding blueline to the numbers either. That was something I was taught at ATP that I had to unlearn. :D

Note that the speed at which you'll be demonstrating slow flight will be BELOW Vsse (or at least it is in my Baron), so make sure your MEI isn't chopping engines on you intentionally. Brief beforehand unless you like unrecoverable spins.

If you dig (or search the PDF) in the manual, you can find a very large-font prohibition against intentional engine cuts below Vsse. This should supercede anyone else's argument to do engine cuts slower, including the DPE's if it comes to that.
Click to expand...

Yep. Engine cuts near Vsse was probably the biggest emphasis during my ME Instructor checkride. Following the AFM/POH for demonstrating slow flight and engine failures has more significance for some airplanes with high stall speeds... Getting close to stall speed is OK for single engine training, but the "indications of a stall" per the ACS is very appropriate for ME training...
 
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