#7b: Climbs and Descents
To determine your ability to maintain safe flight control during climbs and descents.
While this is not a separate flight test exercise, it will be incorporated in the general assessment made by the Examiner.
You will be asked to climb and descend to specified altitudes.
Assessment is based on the following:
- maintain airspeed within ± 10 knots;
- maintain heading within ± 10°; and
- maintain altitude within ± 100 feet.
Climbs and descents are essentially the same procedures as those in single engine aircraft, but there are two exceptions unique to multi-engine flying—the use of the propeller controls, and the use of the cowl flaps. In fact, neither of these devices are used during descents, so we are really concerned with climbing procedures.
Let us first quickly deal with the descent. We all know that the rate of descent is governed with power inputs—this, of course, assumes that the pilot keeps airspeed constant. What you may want to make note of, however, is that 1 “MP reduction on the throttle levers will produce approximately 100’ per minute descent.1 The effect of this reduction will generally vary with loading, but it is a good starting point—after you reduce the throttles a specified amount, you can observe the VSI and make fine-tuning adjustments of the throttle. A comfortable rate of descent is approximately 500’/min., so from a cruise power setting of, for example, 23”MP, you should power back to about 18” per side. The only other thing to keep in mind is that, except for a few occasions, never close the throttles entirely during a descent, as this can cause damage to those very expensive engines. What exceptions are there? Well, we have to do stall practice, so the throttles must be closed then. We will also practise emergency descents.2 More often, however, closing of the throttles may be required on final approach—here it is more critical to use whatever throttle inputs are required to maintain accurately the glide path.3
Remember too that if you want to descend at a reduced speed, the speed reduction should be made prior to lower the nose. It is especially difficult in Seneca to attempt to change speed and altitude simultaneously.
Be sure, as well, to anticipate the need for extra power if levelling at the bottom of a descent is required with the flaps and gear down. While 16”MP will keep the aircraft purring along in the downwind leg with Flaps 10°, this is not the case if the gear and more flap are extended—perhaps 18 to 20”MP will be required.
By the way, students must make periodic gentle turns during climbs and descents, sufficient to take the aircraft 30° either side of the planned track—Instructors get extremely nervous if they don’t see these clearing turns, and the last thing you want is a nervous Instructor! You will, of course, remember the high risk of collision during climbs and descents, and you will be absolutely shocked at the reduced visibility caused by those big nacelles (famous for being in the exact spot that you want to look when sightseeing, and the spot you want to use for scanning traffic).4
With respect to climbs, the two most important concerns are 1) overstraining the engine by using too coarse a propeller pitch, and 2) overheating the engine. Both will spell trouble for those engines and your safety, and both can be easily avoided by following some basic procedures.
In simple terms, using too coarse a propeller pitch will occur whenever the manifold pressure is allowed to exceed RPM. Our equally simple rule is that when we are entering a climb, we anticipate the need to apply additional power and first advancing the propellers to 2500 RPM. After this has been done you can then advance the throttle, but you are limited to 25”MP.5 The requirement to lead with the propeller controls is equivalent to selecting a higher gear while going up a hill in an automobile equipped with a standard transmission. Don’t forget that your manifold pressure drops off 1”MP per 1000’ of climb, so you will periodically have to advance the throttles during the climb to maintain climb power.6 It does not take a lot of altitude before you can safely apply full power and not exceed 25”MP.7 It goes without saying that if you want to climb at a continuous rate you must be vigilant to add an inch of MP every 1000’ or so if you want to maintain a constant power setting. So the sequence for a climb appears to be as follows:
- Raise the nose smoothly to the desired pitch.
- Advance the propellers smoothly from the cruise setting to the climb setting—usually 2500 RPM setting.8
- Now advance the throttles so as to produce climb power—usually 25”MP or full power (provided 25”MP. is not exceeded).
Now the only additional steps we must add here concern the engine temperatures during the climb. Overall, remember that temperature is something that builds or accumulates, so you want to take preventative actions before the cylinder temperature gauges start to rise rapidly—it takes very little time for them to red line, and once they get excessively hot, it is very difficult to get them cooled again. First, we can advance or enrich the mixtures just prior to entering a climb; this has the effect of cooling the flow of air and fuel entering the head and cylinders. Second, we can open the cowl flaps—obviously effective for cooling as a greater volume of cool ambient air is allowed to circulate under the cowling. As a rule, you must carefully monitor EGT during a climb. Whenever the climb speed is reduced to 120 MPH or less, the cowl flaps should be fully opened. If the climb speed is greater than 120 MPH, then the cowl flaps should be opened progressively (one notch at a time) in accordance with temperature indications.
So let us now establish a refined final version of the climb sequence:
- Smoothly raise the nose to climb pitch.
- Enrich the mixtures.
- Advance the propeller levers smoothly and carefully to 2500 RPM.
- Set Climb power.
- Trim as necessary.
- Open cowl flaps in accordance with climb speed.
In a turbo-charged climb the increase in EGT is so incredibly rapid that the mixtures must be advanced before turbocharger power is engaged.
Note that rudder inputs will not be required, as they will be in the case of a single-engine aircraft and the effects of asymmetric thrust.
Be aware that you must avoid “head-in-the-cockpit” syndrome here, as there is considerable demand on precision control of both flight and engine instruments.
1 This is roughly equivalent to the fixed-pitch rule that a 100 RPM drop will produce approximately 100’ per minute descent.
2 See p. 4-4 of the POH supplement pertaining to the RayJay Turbochargers.
3 The need to close the throttle owing to poor final-approach planning, however, will not be regarded lightly by your company Chief Pilot, especially if you are flying aircraft with automatic turbocharger systems—shock cooling of the engine will quickly crack a cylinder.
4 See Footnote # 57 regarding collision avoidance.
5 Unless emergency power—sometimes called “radar power” (indicating that the thrust levers of a jet have been pushed to the weather radar screen)—is required.
6 The reverse, of course, occurs during a descent, in which a periodic throttle reduction is required to compensate for an increase in ambient pressure.
7 You can consult the Power Setting Table that appears on p. 9-16 of the POH for information on this.
8 Remember that the propeller controls are very sensitive and you must be especially smooth and controlled in finger control.