H O F T E C
Pilot Operating Handbooks (POH) used to be thin documents for aircraft certified in the 1940ís, 50ís and 60ís. Gradually, in the interest of enhancing safety, the certification requirements demanded increasing detail to be published. It is part of the Type Certification process that a POH be created and approved along with the rest of the aircraft as the manufacturer seeks Type Approval for his product.
The POH gives the pilot vital operating information. Among the varied information are details regarding aircraft performance, maintenance procedures and systems characteristics. To operate the aircraft safely and legally the requirements outlined in the POH have to be observed by the pilot. The POH is a legal document in addition to the operating rules stipulated by the Canadian Aviation regulations (CARs).
Homebuilt aircraft and Ultralights are not required to have a POH because these aircraft do not have a Type Certificate in the first place. Nevertheless, many designers, manufacturers and kit producers offer their clientele a modicum of pilot operating instructions. They do this if for no other reason than to protect the reputation of their product. Additionally, many organizations and Type Clubs supplement the vast experience gained by the builders and flyers of these products to help owners and pilots enjoy their aircraft more, and to be a source of wisdom, parts and safety advice.
Information is good, and we live in an age where access to all kinds of information appears limitless. However, the downside is that anyone can add to the pool of information regardless of their qualification. Some of what is passed off as information is actually only opinion. That can cause grief if we cannot validate 'information' from unknown sources. Our inability also to remove information (specifically poor information) is problematic. Therein lies the problem. How do we recognize bad advice?
When a designer of a Type Certificated aircraft publishes a POH, the data and procedures therein had to be demonstrated repetitively. The information was created to be for the average operator - not for a 'Top Gun'. The numbers and procedures are conservative and proven and often take factors into account of which the average weekend pilot may not have considered, oversights which could lead to trouble.
Let me mention some which I have come across, both on homebuilts and on certified aircraft, touted by various suppliers and fellow pilots. One is the addition of vortex generators or other high lift devices, added in an effort to be able to fly more slowly. The addition of some of these devices cause the wing to produce the same lift at a lower speed. However, and often forgotten, is that at this lower speed the control and stabilizing surfaces - fin/rudder, stabilizer/elevators and ailerons, are also operating at lower speed and therefore are less able to control the aircraft. That lower effectiveness can be problematic at extreme centers of gravity positions and in the event where an abrupt manoeuvre is required, such as a quick pull back to check sink before hitting a runway.
Another is advice found on some type club sites which indicate that an airplane may be safely operated at approach speeds less than POH values. These opinions may be valid, but at what center of gravity positions and flap angles, for example? Power on or power off? Imagine approaching at 55 mph instead of the published 60 mph. With some high lift device the wing may be producing the same lift. But is the elevator able to rotate the aircraft nose up as quickly at the lower airspeed? Will gust and crosswind corrections be as effective? Likely not. As well, at 55 mph the airplane has 20% less kinetic energy stored in it, energy which at 60 mph would have been available to climb over perhaps a fence or other obstruction. Few people consider the loss of options offered at a lower speed. When you are close to the ground is not where you wish to discover facts about your airplane.
There are other examples of opinion in the field. Among them is the use of car gasoline. Few people I know who avail themselves of the Mogas STC actually test each batch of car gasoline for alcohol content they add, contrary to the provisions of the STC. Inevitably someone always quotes a story of someone who has operated safely for thousands of hours on car gas. On the other hand, overhaul shops tell you with certainty which engines have operated on Mogas versus Avgas. Neither of the big engine manufacturers has ever admitted to the use of other than Avgas as being safe.
Letís be careful before we disregard POH advice which manufacturers have spent a lot of money on developing for our safety.
Frank Hofmann, AME
EAA Technical Counsellor
Eastern Vice Chair, COPA