Acute fatigue: How you physically and mentally feel at the end of a long day.
Chronic fatigue: Long-term fatigue which has serious physiological and psychological effects.
Performance degradation due to acute fatigue can be correlated to blood alcohol level.

• 17 hours awake = 0.05% blood alcohol level
  
• 20 hours awake = 0.10% blood alcohol level

We clearly would not fly if we were intoxicated. Why would we fly if our judgment was equally impaired simply because we are tired?  One of the best mitigation strategies is to take a short nap. The effects of acute fatigue can be temporarily mitigated with the strategic use of caffeine.
 
The longer a person is awake, the sleep urge and need becomes stronger. The pressure to sleep grows more intense as the day progresses, then dissipates when one sleeps at night.

As one extends wakefulness into routine sleep hours, the urge to sleep increases.  The primary factor that affects alertness is the number of hours continuously awake. At about the 16 hour mark, sleepiness begins to affect performance of the average individual. 

Studies show that after 18 hours of wakefulness, participants showed a 30% decrement in performance and problem-solving ability.

Chronic fatigue can be caused by multiple back-to-back long days with less than the required sleep each night. This leads to serious performance degradations. Performance degradations include the following:

• Reaction time decreases by 25%.
• Mood changes 100% (from good to bad.)
• Attention lapses increase five-fold.
• Lethargy and apathy increase by 50%.
• Judgement and decision making decrease by 50%.
• Memory decreases by 20%.
• Communication decreases by 30%.
  

Those performance degradations in the cockpit have manifested themselves in the following ways:

• Lower standards of performance unconsciously become acceptable.
• Attentional resources are difficult to divide effectively.
  
• Performance becomes inconsistent.
• The ability to reason logically is impaired.
  

,I do a lot of Multi engine ratings in several types of airplanes from several schools.  It's amazing how differently things get taught between different schools using the same airplane.  As I posted in the Commercial Single Engine earlier, I encourage everyone to review the appropriate ACS and the Airplane Flying Handbook.

I also encourage everyone to use and follow the emergency procedures as described in the airplane POH.  I have seen several applicants deviate from the check list and unfortunately screw things up to the point that the airplane is no longer in their control.  Even a few applicants have failed to use the checklist other than for the run up.  Using the checklist is a part of good Airmanship.

Here's one situation that continually creeps up on multi engine rides.  The applicant straight and level at 5000 feet when an engine fails.  As they go threw the engine out drill they let the altitude and or heading drift outside of ACS tolerances.  The applicant is so focused on the engine failure that they for get to fly the airplane.  So hold heading and altitude while you do the engine out drill.  If you are above the single engine service ceiling, hold altitude until the airplane slows down to Vyse and then allow it to drift down at Vyse. 

Another problem area is shooting the engine out instrument approach.  I usually ask what speed and configuration you will fly this approach at.  Unfortunately, most fail to fly what they tell me they will.  The biggest issue is they are usually 20 to 30 kts too fast.  The second issue is they fail to maintain vertical and lateral guidance within ACS requirements.  I recommend developing a profile that uses minimum work load to fly a stabilized approach at  Vyse+10 kts (no slower than Vyse) with the gear down and no more than 10-15 degrees of flap.

Last piece of advice....Above all else.....Fly the Airplane!

The Commercial ACS was updated last year with a couple of new items and clarifications.  I'll cover a couple of those items here.

You'll note that the ACS describes the tolerances for each maneuver and not how to do a maneuver.  In the ACS at the top of each Task the FAA list the References.  In these references the FAA describes how to do each maneuver.  During a check ride the FAA and the Examiner expect the applicant to perform each maneuver as described in the appropriate FAA reference material and to the standards listed in the ACS.  

Several maneuvers that are frequently not performed in accordance with FAA reference material are the Power off 180 degree accuracy landing, 8s on pylons and the power off stall.  I erge everyone to review the FAA's Airplane Flying Handbook for correct description of these maneuvers.

I'd also like to point out a new requirement in the ACS (it appears in both the private and commercial).  If you look in the Area of Operation labeled "Takeoffs, Landings and Go-Arounds"  under "Skills"  you will see the phrase "Touch down at the proper pitch attitude...".  This is important.  In the past we would see applicants try to force the airplane on the runway to make the desired spot.  In attempting to do that the airplane would hit the ground flat on all 3 wheels (not talking tailwheel airplanes here).  Landing flat is not good techniques and could easily damage the airplane. 

I'd like to emphasis some of the wording on landings from the ACS.  " Touch down at a proper pitch attitude with in XXX feet beyond or on the specified point, ....... with NO side drift, minimum float and with the airplane's longitudinal axis aligned with and over the runway centerline.  In reality, this is the description of a good landing.  Notice the don't say anything about how smooth it must be.  Don't worry about trying to role it on.