U.S. Department
of Transportation

Federal Aviation

St. Louis
Flight Standards District Office

10801 Pear Tree Lane
Suite 200
St. Ann, Missouri 63074


August 2004 




Thought for the month..... An airman with a timepiece always knows the time.
An airman with two timepieces is never sure.

Where does the time go?. How do you log your time? Sure, I know it goes into a pilot log or maintenance record, but where does it come from? If we log two hours of flight time, does that mean the aircraft was in the air for two hours? When a 100-hour inspection is performed on an aircraft, is the 100 hours in operation based on the tachometer reading? Hobbs meter? Sun dial?

Part 1 of the Federal Aviation Regulations contains definitions of terms used. It defines the following:

Flight time means:
(1) Pilot time that commences when an aircraft moves under its own power for the purpose of flight and ends when the aircraft comes to rest after landing; or
(2) For a glider without self-launch capability, pilot time that commences when the glider is towed for the purpose of flight and ends when the glider comes to rest after landing.

Time in service, with respect to maintenance time records, means the time from the moment an aircraft leaves the surface of the earth until it touches it at the next point of landing.

Neither definition talks about tachometers or hobbs meters, and clearly, they are not the same times. The term, "block to block" is a convenient way of describing "flight time". It means that the aircraft has been started and may have been running for some period of time, but "flight time" doesn't begin until it moves for the purpose of flight or, moves out of the blocks (chocks). The tach will certainly have begun recording time as soon as the engine was started, and the hobbs meter, depending on how it is installed, may have begun recording as soon as power was applied to the aircraft. "Flight time" ends when the aircraft terminates at its parking location (blocks) even if the engine continues to be operated for some period of time. Pilots, who log "flight time" based on tachometer readings or a hobbs meter, may be in error.

"Time in service" on the other hand, is defined as the time from the moment of takeoff to the moment of touchdown. This also is probably not represented accurately by either a tachometer reading or hobbs meter. Some operators have installed a "squat" switch on their aircraft with retractable landing gear. As soon as the weight is off the wheels, a recorder begins tracking time until the aircraft touches down again. As long as the aircraft isn't landed gear up, this is probably the most accurate method of keeping track of time in service. Operators, who base required inspections on tachometer or hobbs meter readings, are probably cheating themselves out of several hours a year, depending on how much flying is done in the aircraft. Aircraft operated at busy airports may spend considerable time with engines running before takeoff and after landing as they taxi to and from the parking area, or hold on the ramp while a pilot picks up a clearance and performs a run up.

In most cases, flight time and time in service for a helicopter are the same. In the case of a helicopter with wheels, it is conceivable that the aircraft may spend some time taxiing in or out of parking areas that should not be applied against the time in service. This might be an important factor since many expensive helicopter parts are time limited. Losing 10 hours over a 2000-hour life might be significant.

The reason most places use tach or hobbs time is because to log time correctly would require the operator to accurately record block out/in, and takeoff and touchdown times. Who cares anyway? Maybe after 100 hours of logging flight time from the tach, a pilot has accumulated 1 hour of extra time. What's the big deal? It's not like anyone is loading the logbook with several hundred hours of Parker Pen time. Perhaps not. But if someone were trying to make an issue of an airman's competency, it would certainly be an easy way to start by proving that we don't even know how to properly log time. Too many sources of time can make us uncertain about which is correct.

Upcoming Events

August 12
Grecian Steak House
1108 W. South By Pass
Kennett, MO
The Successful Cross Country
7-9:30 P.M.

August 18
Wings of Hope Hangar
18590 Edison Av
Spirit of St. Louis Airport
Light Sport Pilot and Light Sport Aircraft
5 to 8:00 P.M

August 19
Mid-Coast Training Center
18 Mark Allen Drive
St. Louis Downtown Airport
Part 135 Safety and Standardization Meeting

August 26
Mid-Coast Training Center
18 Mark Allen Drive
St. Louis Downtown Airport
The Successful Cross Country
7 - 9:30 P.M.

September 27
Florissant Valley College
3400 Pershall Rd., St. Louis 63135
GPS: Beyond Direct
AOPA Air Safety Foundation
7 - 9 P.M.

October 23
Mid-Coast Training Center
18 Mark Allen Drive
St. Louis Downtown Airport
8th Annual Helicopter Safety Seminar
9 A.M. to 4 P.M

Register at http//faasafety.gov for E-mail notification of safety seminars in the St. Louis District.

Operations Safety Program Manager
1-800-322-8876 extension 4835