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Let's assume that you took off in a seminole and had one engine suddenly failed, say, at 400 feet AGL. You right away pitch for 88 knots (Vyse) to keep climbing, yet you start to descend because the density altitude is too high. In this situation, would pitching up for 82 knots (Vxse) give me a chance to climb back? Or would it only give me a greater descent rate?

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  • $\begingroup$ Vyse is your best rate. If you cannot climb at your best rate you cannot climb. If Vyse gives you -100fpm, Vxse will give you less than -100fpm (a faster descent). $\endgroup$ – acpilot Apr 8 '17 at 14:00
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I'd recommend reviewing Chart 5-23 from the PA-44 POH - Climb performance one engine operating - gear up for specific numbers based on aircraft weight and atmospherics.

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If you're not seeing a positive rate of climb at your best rate of climb, single engine airspeed, then you're not going to see it at the best angle of climb airspeed single engine either. By definition, Vyse is the best rate of climb that you're going to see on a single engine; any other airspeed, including Vxse, is going to give you a lower rate of climb, or greater rate of descent if a positive rate is not possible. And attempting to acquire and hold Vxse you're getting close to the reverse side of the power curve, combined with ever decreasing rudder authority, it would be easy to have the aircraft drop below Vmc and depart from controlled flight.

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    $\begingroup$ Thank you for your answer. I posed the same question to my multi instructor lately and he told me in theory no airspeed would give you a climb if Vyse can't, but he added I should do whatever is necessary in emergencies and pitch for Vxse if it gives me a climb, which got me confused. Thanks. $\endgroup$ – lemonincider Apr 9 '17 at 7:38
  • $\begingroup$ Vx increases as the thrust margin reduces until it equals Vy at absolute ceiling (and then for gliding, Vx, as best glide angle speed, is higher then Vy). This works the same with both engines and single engine, just the values are different. $\endgroup$ – Jan Hudec Apr 9 '17 at 19:58

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