Deviating from the POH

An instructor friend of mine wrote:

You mentioned in a recent presentation that the only things that are of a legal nature in the Pilots Operating Handbook (POH) are those things listed in the Limitations section. Otherwise the pilot can basically do as they please (or words to that effect). I think I get the general idea of what you meant. One of my students, however, interpreted this to mean it is quite acceptable to:

  • Take off and bring the power back to 26′ and 2400rpm as soon as you are airborne.
  • Use reduced power for take off as you may not require full power with a long runway.
  • Retract the undercarriage as soon as the aircraft leaves the ground.
  • Us a starting technique not found in the POH……. and so on!It becomes difficult when trying to train someone and they are told old wives tales that conflict with the POH. I realize that there is a fine line between legal and what is recommended, in some cases. I am not sure your comment was meant to be taken so literally. Could you elaborate so I may dispel this issue?

    My friend’s concern is a very real one. There are a lot of unsubstantiated myths (commonly called ‘Old Wive’s Tales,’ or OWTs) about airplane operation passed on from generation to generation of pilot that really need to be dispelled. In many cases, especially engine operating theory, a lot has changed since most Pilots Operating Handbooks were originally written and better guidance may now be available. And the majority of POHs contain procedures and performance information only for a small series of optimal conditions. How can pilots (and the instructors that train them) sort through the maze of POH requirements and recommendations, and incorporate the latest information for managing their airplanes?

    What’s ‘Required,’ and What’s ‘Recommended?’
    There are many arguments about what is ‘required’ when operating an airplane, and many ideas about operation that have emerged as experience and science has advanced in the time since most POHs were first written. To better understand this, it’s valuable to review what is ‘approved’ by the certifying authorities and what is merely ‘accepted.’

    Section II, Limitations (and the corresponding Limitations of any POH Supplements applying to modifications under Supplemental Type Certificates, or STCs) is ‘approved’ by the U.S. Federal Aviation Administration. This means (at least for our U.S. readers) that the stated Limitations have the full force and effect of a Federal Aviation Regulation (FAR). Any deviation from operation within the stated Limitations may be evidence of ‘careless and reckless operation,’ punishable under Federal law. Examples of this are operating over maximum gross weight, taking off with less than minimum fuel, purposely violating engine temperature restrictions, taking off or landing while an auxiliary fuel tank is selected, etc.

    INSIDER’S TIP: You can see that the sorts of things that become Limitations are those that can lead to accidents–and usually have in the past.

    All other parts of the POH are ‘accepted’ by the FAA but not ‘approved.’ These sections of the POH do not have the status of Federal law. They represent the manufacturer’s best recommendations for operating the airplane at the time the POH was written. Other techniques and procedures may be equally acceptable (or even desirable) so long as they result in the desired outcome-a mishap-free flight that leaves the airplane, its engine and systems in good condition.

    For instance, POHs for many airplane makes and models provide takeoff data only for a ‘paved, level, dry runway surface.’ Of course we have the authority to utilize unpaved, sloped, and/or wet runways as long as we determine to the best of our ability beforehand that adequate runway length is available for takeoff. Similarly, our POHs usually contain just a few cruise power charts with narrowly defined (and superseded-by-science) guidance for mixture control, yet we have the option of selecting different power combinations and using different techniques to achieve ‘desired outcome’ flight while remaining within the legal Limitations.

    Intelligent Deviation
    As my friend said, what is ‘legal’ may not necessarily be SAFE. For instance, unless a Limitation requires it, reducing engine power as soon as the airplane is airborne is ‘approved’ (or more correctly, ‘not unapproved’), but it may create an unsafe climb rate, insufficient to clear obstacles. It almost certainly will result in higher cylinder temperatures and internal cylinder pressures (ICPs) that may reduce engine longevity and make an in-flight failure more likely. A reduced-power takeoff in most piston airplanes will greatly degrade airplane performance when you need it most (slow and close to the ground), while snatching up the landing gear too quickly invites a gear collapse on the runway if the airplane isn’t fully airborne or settles back toward the runway.

    Conversely, individual airplanes often have quirks that make starting the engine(s) easier with a few pilot-learned ‘tricks.’ Running a properly balanced engine lean of peak EGT is not mentioned in the most POHs but done properly is arguably a better way to achieve engine longevity than the POH ‘recommendations.’ So long as such operation does not violate any Limitations, it is ‘not unapproved,’ and the pilot can ‘legally’ elect to use the technique.

    Incorporating Limitations, Recommendations and Experience
    The way I teach pilots to incorporate Limitations, Recommendations, and the result of their own and others’ Experience, then, is:

  • For all operating techniques, the POH (and similar guidance from engine and component manufacturers) is the ultimate guide to flying the airplane unless the pilot has good reason to deviate through experience and learning.
  • So long as a non-POH operating technique or procedure does not violate Limitations (and of course other Air Regulations), it is permissible and ‘legal.’
  • When deviating from the POH the pilot accepts full responsibility for determining the result (both short- and long-term) will be satisfactory-that it will achieve the ‘desired outcome.’
  • Remember that the POH was written by experts on the equipment using the best information available at the time of writing. Carefully consider your reasoning and justification for using any technique that differs from that contained in the POH.
  • Do not use a non-POH technique unless personal experience or learning gives you a reasonable ability to predict the results.BOTTOM LINE: The Pilots Operating Handbook and Federal Air Regulations give us a lot of freedom as to how we operate our airplanes and their systems. It’s up to you to continually learn and evaluate whether ‘they way it’s always been done’ is best for your given situation.