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Caveat Emptor:
Doing A Technical Analysis

One + One = Two… except for large values of one. That math joke refers to rounding off numbers. When rounding off to whole numbers- we usually round to the nearest value. So 1.45 rounds off to 1 while 1.55 rounds off to 2. So 1.45 + 1.45 = 2.90 which itself rounds off to 3- unless you round off early and incorrectly. Then 1.45 rounds off to 1 and you get 1 + 1 = (in this case) 3. I didn't say it was a great math joke- but it helps illustrate the trouble we can get into with numbers.

For a more complex example- we only need to look at aircraft performance and technical specifications. A detailed technical analysis is very important when selecting an aircraft. A quick look at some numbers can lead to a false conclusion. While in many instances- your initial instinct is correct- the technical analysis can reveal other alternatives- some of which may be better suited for your mission than the initial pick.

The focus of an aircraft technical analysis is on size- features- range and performance. Your mission will drive these requirements. Many of the aircraft acquisition plans we do focus on requirements such as passenger seating- cabin size and range. The general way to approach this is to:

● Determine the most (likely) demanding payload- range- cabin size and/or passenger seating requirement as defined by your key mission.
● Compare those mandatory requirements against the capabilities of a range of aircraft.
● Eliminate all those aircraft that do not meet the requirements.
● Eliminate those aircraft that are vastly more capable than required. The cost of acquisition and ownership goes up dramatically as size- range and speed increase.

Here is where the match can get fuzzy: If you need a range of 1-450 nautical miles with four passengers- what exactly do you mean? For the range- do you mean VFR range? IFR range? IFR range with what sort of alternate airport? A 100nm alternate; 200 nm alternate; something else? In general- literature on turboprops and very light and light jets refer to ranges with a 100nm alternate that follows the NBAA IFR Fuel Reserve format. Somewhere in the light jet category- the 200nm alternate becomes 'standard.'

Four passengers are four passengers- right? Yes and no... Most published data assumes each passenger (with bags) weights 200 lbs. But some data may refer to 170 lb passengers- while the FAA and airline data suggest the average American airline passenger with bags runs well over 200lbs.

We did an analysis for a company in the construction industry. Their executives looked like 'construction guys' and weighed somewhere around 240 lbs each. So when doing your passenger analysis- take into account issues like whether you are carrying ballerinas or football players!

The same passenger weight comment applies to the Basic Operating Weight (BOW) of the aircraft as well. BOW includes crew. Is your aircraft to be flown single pilot or with two pilots? That 200 lb difference in weight can- when carrying near-full loads- mean 200 lbs plus/minus on the fuel load- or almost 30 gallons. If your aircraft burns 120 gallons/hour at 240 knots- 30 gallons is 20 minutes or 60 nm. That may be enough to move the aircraft from acceptable to not acceptable due to its range.

Much of the published data on aircraft are 'maximums' and may not be achievable under most conditions. As an example- the Certified Ceiling is the maximum ceiling the aircraft is certified to be able to operate safely. That does not mean that the aircraft can climb that high on a routine basis. I've seen many aircraft that have to weigh close to their BOW to be able to climb to their certified ceiling.

When evaluating aircraft performance and technical specifications- you need to understand the assumptions that went into the number - especially as they relate to your aircraft requirements. Finally- when comparing data for different aircraft- you need to have the data based on the same assumptions - the old ‘apples-to-apples’ comparison.

David Wyndham is an owner of Conklin & de Decker. The mission of Conklin & de Decker is to furnish the general aviation industry with objective and impartial information in the form of professionally developed and supported products and services- enabling its clients to make more informed decisions when dealing with the purchase and operation of aircraft. With over 1-800 clients in 90 countries around the world- Conklin & de Decker combines aviation experience with proven business practices. More information from www.conklindd.com; Tel: +1 508 255 5975

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