Aim: To determine your ability to recognize power-off stalls and accomplish a recovery smoothly and positively with a minimal loss of altitude.
At an operationally safe altitude—i.e., an altitude that will allow a recovery at or above the altitude recommended by the manufacturer or at 2000 AGL, whichever is higher—you will be asked to enter a stall from straight and level flight with the power on both engines set to idle.
You will be asked to perform two stalls, the first from a cruise configuration (clean), and the second in a landing configuration (dirty). You are to be cautious not to enter the stall from an excessively high nose attitude.
Assessment of your skill here will be based on the following:
Discussion
Once you are established at the altitude that you are planning to do the stall sequences, bring the power back to a setting that keeps the aircraft speed reduced—say 16 to 17”MP. This creates some important advantages. Firstly, when power is eventually reduced to idle, there is less time for prolonged shock cooling to the engines, as the stall is achieved in a shorter time. Secondly, since you are entering the stall sequence at a reduced speed, there is less need for drastic trim changes as the aircraft slows—this makes it easier to maintain an assigned altitude, and it will make it easier to partially trim off the excess control column weight—surprisingly heavy—that is experienced just prior to the stall. Thirdly, the power quadrant must be properly set for stall recovery—the mixtures must be set full rich, and the propellers set to maximum RPM—and the reduced speed when preparing for the stall sequences will ensure the propellers won’t “scream” when maximum RPM is set prior to stall entry (as they would if this RPM setting were selected in the cruise speed range).
The HASEL check must be completed here, and in so doing, here are some points to remember:
When ready to reduce power for the entry, be sure you use a prominent landmark for tracking reference.
Reduce power smoothly, but continuously—the slower reduction will help slow down the required adjustments of pitch and trim.
The exercise specifically prohibits you from climbing above your assigned altitude, which of course will occur if you pitch-up to meet the stall. Concentrate on the visual pitch reference provided by the glareshield in relation to the natural horizon. During the transition to the stall, your adjustment of the apparent distance between the glareshield and the horizon should be based on instrument indications provided by the altimeter and the vertical speed indicator.
Get ready for lots of horn sounds, especially during the demonstration of a clean stall—you will get both the gear horn and the stall horn (the combination of which can be quite disheartening).
The most important component of this exercise—and the feature which makes the multi-engine stall different from the single-engine stall—is the use of power inputs at the recovery phase. Specifically, remember that a stall entails flight below Vmc. We know that the application of power below Vmc is done with potential risk. Should the engines fail to respond with symmetric thrust—especially if full power is applied—the results could be a Vmc spin. The solution is to “guard Vmc” during the stall recovery. The operative rule here is that full power must never be applied during a stall when the ASI is below red-line Vmc. Now you are going to ask: How the heck am I suppose to eyeball the ASI during a stall recovery? The answer is that you shouldn’t have to do this if you execute the recovery correctly. First, in a stall recovery, reduce the pitch angle as you would in any normal stall recovery, and simultaneously add only ½-power. This will immediately start the positive movement of the ASI as the aircraft’s momentum changes. Then wait for a full two seconds—approximately—before you smoothly input full power. If you time the full-power selection properly, the ASI needle will be just sweeping positively past the red-line Vmc as you are leave the ½-power mark for the full-power mark. It becomes a work of art when you do it right. It is still important to cross-check the ASI as full power is selected, but this is only for confirmation. As with all multi-engine power changes, smoothness is the everlasting key, so be sure to nurse the throttle levers accordingly. It goes without saying that you must keep the two throttle levers properly paired in your right hand.
When preparing for the landing-configuration stall sequence, the flaps and gear must be extended—look good, here, and use the standard sequence—flaps 10°, gear down, flaps 25°, then flaps 40°. To maintain the same slow speed you used for preparation and entry into the clean stalls, you will have to compensate for the increased drag with increased power—from the 16-17”MP used prior to the clean stall, you will now have to select 18-19”MP. Be smooth but quick here, selecting the compensating power increase immediately the gear is selected down and the final 40° of flap set. Note that the clearing turn should only be started after the drag is set—should you accomplish the clearing turn before lowering the flaps and gear, the time delay will invalidate the clearing turn.
With respect to the landing-configuration stall, there are a couple of variations of which you should take careful note. First, because the aircraft is enveloped in lots of drag, a more aggressive pitch-down response will be required as the recovery is initiated. By “more aggressive,” it does not mean that the control column should be pushed forward faster—this would undermine the need for smooth inputs. Instead, it is meant that you will have to lower the nose further downward to permit the aircraft to effectively accelerate despite the increase drag items—40° flaps and gear extended. The recovery routine with respect to power inputs is the same as in the clean stall sequence, but if you fail to push the nose forward sufficiently, the “two-second” power delay used for the clean recovery will be insufficient for the ASI needle to transition past safely beyond the red-line Vmc. Note that a cross-check of the ASI just prior to full-power inputs is more critical with landing-configuration stalls—owing, obviously, to the increased drag. Note also that the climb-recovery angle of attack will be less than in the clean stall. Rather than matching the glareshield to the horizon for the recovery climb (as was the case in the clean-stall recovery), the glareshield should be placed slightly lower—say an inch below the horizon as viewed from the pilot seat. Once full power and the proper climb angle is established, the flaps and gear should be recovered using the standard sequence—flaps from 40° to 25°, gear retracted, flaps from 25° to 10°, then clean.
Safety
Be sure the HASEL is conducted thoroughly and efficiently.
Of course, whenever you perform stalls, be ready for the spin, for which the Seneca spin recovery is conventional.
1 Failure to conduct a clearing turn prior to individual stall demonstration is grounds for a severe response from the Examiner.
