Logbook Research: It's not just an AD search any more

Logbook Research

By Joe Hertzler

The maintenance records of an aircraft are the single most important factor considered when evaluating an aircraft for purchase. The value of an aircraft can be affected significantly when maintenance records are incomplete, missing, or just plain sloppy.

This is the first of a two-part series that will outline and discuss the logbook research process in an effort to help you identify inadequacies in maintenance records that can impact an aircraft's value. In this issue, we will look at organizing the records in preparation of the research and some of the things to consider.

Are the records complete?
Once you get your hands on the logbooks, you first need to know if all the records are there. A complete set of maintenance records from the standpoint of the FAA is defined by 14 CFR Part 91.417. However, that outline should be considered a minimum requirement. You will find with the records, among other things, bound logbooks, maintenance release documents (yellow tags and 8130-3's), FAA form 337's, Airworthiness Directive Compliance records, and many times some sort of compliance status report created by someone else who researched the records previously.

Note: If you find a status report that someone else created, we recommend that you use it solely as a guide to direct you to legal signoff statements contained in the official logbooks, and even then, not until you have completed a second pass through all the logbooks.

First write down the aircraft make, model, and serial number and list below it each of the Class I Products (i.e. each engine and propeller) (Ref CFR 21.321, (b)), by make, model, and serial number, currently installed on the aircraft. It is a good idea to visually verify the part numbers and serial numbers of the aircraft, each engine and each propeller to make sure they match what the records say.

Next, separate the maintenance records for the aircraft, each engine, and each propeller into individual areas on the table. Place the logbooks for each in order by date and on a sheet of paper record the start and end date for each logbook.

Warning: Many of the old bound logbooks have separate areas for maintenance and inspection. In those cases, the work sometimes does not flow through the logbook from beginning to end. Some technicians use the logbook as designed and enter inspections in the inspection section and maintenance in the maintenance section, which places the entries out of chronological order.

After recording the timeline for the aircraft, engines, and propellers logbooks, look closely to identify any significant gaps. Records should flow from one logbook to the next with no significant gap. When a significant gap is found, check the gap in aircraft time as well. Sometimes an aircraft will sit for a while and not get used. However, if there is a six-month gap along with 200 or 300 hours of utilization or more, for example, without any maintenance, make a note of the inconsistency so that questions can be brought up later.

Try to place the maintenance release documents with each applicable logbook, i.e. aircraft, engine, or propeller, so that they are well organized for your research. If you find any FAA form 337 documents, place them in a separate group and order them by date. Many times, the owner of an aircraft will keep the FAA form 337 documents in the aircraft flight manual or operation handbook in the weight and balance section. If the 337's are in the flight manual, we recommend that a copy of each be made and a binder created and kept with the logbooks just for 337 forms. These days, many 337 forms include instructions for continued airworthiness and such instructions should be with the logbooks.

Accurate times and cycles
The next step is to establish the current times and cycles for the aircraft, engines, and propellers. We have many times found an engine to have 500 to 1,000 more or less cycles than the owner thinks, and likewise with hours. Although the aircraft time can usually be derived using the hour meter in conjunction with the maintenance records, the owner should provide the current landing count for the aircraft.

To establish the current times and cycles for each engine and propeller, we recommend the following equation be used:

([Engine Time @ Install] - [Aircraft Time @ Install]) + [Current Aircraft Time] = [Current Engine Time]

To use the equation you must have the most recent installation of each engine and propeller within the component logbook as well as the airframe logbook. It's important to emphasize that the record of the most recent installation must be used. Sometimes it will be an overhaul entry or a hot section inspection or MPI, but just as often the engine or prop can be removed and replaced by a loaner for a repair and then re-installed following the repair.

For each component (engine and propeller) locate the last installation entry and write down the date, total time in service, and total cycles in service. Using those numbers, follow the equation above to derive the current time and cycles for that engine or propeller. Remember to use the same date (installation date) for aircraft and component times.

For example, if the engine time was 2,768.5 total hours and 3,467 total cycles when it was installed on the aircraft, and the aircraft time at installation was 3,567.2 hours and 3,617 landings, and the current aircraft time (today) is 4,724.5 and 4,978 landings, the current engine time and cycles would be derived as follows:

Hours = ([2,768.5] - [3,567.2]) + 4,724.5 = 3,925.8
Cycles = ([3,467] - [3617]) + 4978 = 4828

This reflects the accumulation of time and cycles equal to that of the aircraft since the last installation. In all cases, time in service accumulates the same as the aircraft. In most cases, the engine cycles accumulate the same as aircraft landings. However, in the rare instance that the operator counts the engine cycles differently, the operator's cycle count obviously should be used.

What we have learned through hundreds of records audits is that it's far more likely that you will find an error has been made in the tracking of the engine or propeller times and cycles and that the equation mentioned here will resolve any discrepancies. A large discrepancy in times and cycles, for the engines in particular, can have a substantial cost impact. A rule of thumb number, for example, for a PT6A-42 engine is $50 per hour or per cycle. This assumes that the average overhaul will cost $150,000, and that the average TBO is 3,000 hours (this does not include maintenance between overhauls). So if during research we find that the engine has 500 more hours or cycles than the owner is advertising, that translates into a $25,000 swing in value.

Once you have a good total time and cycles for each component, compare it to the times and cycles provided by the owner and note any discrepancies.

What is the inspection program?
The next step is to determine what inspection program the aircraft is utilizing. The program may be an annual/100-hour program for light piston aircraft, or the complex inspection program recommended by the manufacturer for multi-turbine powered aircraft (Ref 14 CFR Part 91.409). Another possibility is that the aircraft is currently operated under an Air Carrier certificate being maintained in accordance with an Approved Aircraft Inspection Program (AAIP). (For details on possible inspection programs refer to AMT Around the Hangar articles for July, September, and October 2001 also available online at www.amtonline.com).

Once you know the inspection program the aircraft is utilizing, you can compile a list of all of the requirements for that program. The idea is to get a good handle on the program and have it fresh in your mind when you begin reading through the logbooks. Compile the list in a way that will provide space to write down when each item was last accomplished and calculate when it is next due as you read through the logbooks.

Areas that can be more troublesome than others are major modifications. Major modifications generally require some sort of instructions for continued airworthiness (ICA). These instructions will mandate inspections that are required because the aircraft has been modified and the manufacturer's inspection program or other approved inspection program does not cover that area or component of the aircraft.

Another troublesome area is the inspection requirements issued by the engine or propeller manufacturer. Many believe that the aircraft manufacturer inspection program covers all of the engines and propellers. This is simply not the case for the multi-turbine powered aircraft. 14 CFR Part 91.409 (e) includes the requirements contained in the "airframe, engines, propellers, rotors, appliances, survival equipment, and emergency equipment" manufacturers maintenance instructions.

Also, don't forget to identify all of the life-limited components within the aircraft, engine, and propellers along with their life limit and the amount of life remaining. Engine components, in particular, are often overlooked because it's assumed that the parts in the engine will make it to the next hot section inspection or overhaul. People believe that no one would install life limited parts that wouldn't make it to the next access to that area of the engine.

So, by now you should have the logbooks organized in a way that will make the research smooth. You should know the current aircraft time and landings and the times and cycles for each engine and propeller installed. You should also have a copy of the maintenance/inspection program for the aircraft and have generated a list of requirements to be used to document when each item was last done and calculate when each item is next due. Assuming the research is for a multi-turbine-powered aircraft, the list should include inspection requirements for the engines, propellers, and appliances as well as any modifications that have been incorporated as part of an STC of field approval.

Next month, we will work through the actual logbook review process and cover many of the common issues that are found in research such as damage history, improper sign-offs, and required certifications and support documents. AMT

Joe Hertzler is the president of AVTRAK, Inc., based in Aurora, CO. Joe is an Airframe and Powerplant Mechanic with Inspection Authorization and also a Private Pilot.

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