Approach Energy Management

Its finally here. I've met the multi-engine time insurance requirements.  I have what I needed to upgrade to full fledged Captain on the Navajo, so I finally get my upgrade.  Yesterday we did my Captain check ride.  Its wasn't a big deal really, did some aerial work to start off - steep turns, climbing/descending turns, slow flight, stalls.  The usual.  The Navajo is easily the most stable aircraft I've flown.  It was smooth air during our flight, and when I was demonstrating some rate one turns (standard turn of 3°/second) with the airplane properly trimmed I was able to roll into the turn, establish the attitude, and then completely remove my hands from the controls!  The Navajo would maintain a perfectly stabilized bank all on its own and carry itself all the way through the turn without any need for further adjustment.  I've never seen an airplane stable enough to be able to do that.  It makes me look good!

After the air work we reviewed our emergency procedures.  That took us all of an hour.  The ops manual mandates 3 hrs of flight time for an initial PCC (Pilot Competency Check), so we took the time to practice some IFR approaches just for the fun of it.  It was fun to get back into that world again for a little bit and shake off the rust.  The Navajo, being so stable, makes a great platform for IFR practice.  It was also good to really get some practice fine tuning my approach skills in the Navajo.

Whenever I set up my final descents to land, either VFR or IFR I try to plan the approaches in such a way that I only ever need to reduce power, never add more as the approach progresses.  Its not really critical, but it is a lot easier on the turbos, allowing them to spool down gradually with progressively lower power settings.  That and its a good challenge to keep my skills sharp.  It takes planning, judgement and a good knowledge of what power settings the airplane needs so as to not have to increase the power at any point during the approach.

Normally, at the beginning of the descent to land, you start off with the airplane in a clean configuration (flaps & landing gear up) and a cruise power setting (high airspeed), but by short final you should have full flaps set, the landing gear down, and a low power setting sufficient to provide an appropriate descent angle of around 3° and nice slow approach speed.  Its easy enough to set the power to set up your approach angle and  airspeed, but if you set the power to give you the proper descent angle and airspeed BEFORE you have the flaps and gear down, you're going to have to ADD power again later when you lower the landing gear or flaps to account for the increased drag.  With an equal power setting, flaps and gear will always either increase your descent angle (if you maintain the same airspeed), or it will decrease your airspeed (if you maintain the same descent angle).  A stable approach should always have a constant descent angle, so we should strive for that.


The first thing they teach you when you first start flying an airplane is that on approach, power controls the descent angle, attitude (the angle of the nose to the horizon) controls airspeed.  This means that if the current descent angle is going to bring you short of the runway, rather then pulling back and raising the nose (the natural inclination) you need to add power.  Pulling back will reduce your airspeed, so you should only pull back if you need to slow the airspeed, otherwise the potential exists for a stall.  Alternatively if you're going to land long, rather than pushing forward, which will just increase your airspeed and still cause you land long, you must reduce the power.  The concept of "Attitude controls airspeed, power controls glide slope" methodology works quite well for teaching purposes.  It keeps things simple for new pilots who still have to use the cognitive part of their brain to control their approach.  As proficiency increases you learn to do both (control attitude and power) simultaneously as needed to achieve the right approach and right airspeed, and it becomes second nature.  Using power to control glideslope and attitude to control airspeed never ceases to be a safe method for flying an approach even for experience pilots, but it can be sloppy in the sense that it requires constant power adjustments, and small increases in power each time landing gear and flaps are lowered.


So as professional pilots we can take it one step further and rather than just manage our airspeed and approach angle as separate variables, we can focus on energy management as an entire system.  Lowering the flaps and landing gear are removing energy from the system in the form of extra drag, so rather than having to replace it with more energy by adding power, we can plan for it in advance by already having extra energy in the system.  The key to holding extra energy is to do so in the form of carrying extra airspeed at the beginning of our approach.


Now rather than adding power every time we lower the next notch of flaps or landing gear, we want to start our approach with a higher airspeed then what we want to end up with on short final.  In the Navajo for example, or short final we want a stable approach at 120 mph, with full flaps and landing gear down.  That means when we start our approach with a clean configuration (flaps/gear up), we should start with a higher airspeed, perhaps around 150 mph.  In this way each time we introduce more drag into the system by lower gear or flaps, rather than countering the energy loss by adding power, we use the extra drag to our advantage by allowing it to slow us down.  Hopefully if our judgements are correct, by time we have all flaps and landing gear lowered, we're at a stable 120 mph, having never touched the power since we first started our descent.

In this way we're actually simplifying our approach by allowing each new drag element to slow us down rather than adding the extra steps of trying to slow down at the beginning by pulling the power WAY back, and then compensating for it later when we add more drag.  When done properly the engines are happy because they have received consistent inputs, any traffic behind us is happy because we didn't hold them up by dragging our way all the way down the approach at a slow airspeed, and we're happy because our workload is less and we're demonstrating a mastery of our aircraft.