Terms for Hours and Overhaul Alphabet Soup!

Ever look at ads for aircraft and see a bunch of alphabet soup in the description concerning engine time, overhaul time, total time…etc? So what does 4280 TT;  920 SMOH; 1203 STOH; 1234 LMNOP stand for? To help explain this alphabet soup without going into too many details, I created a list for you to review that was based on a conversation I had with a guy who does annuals. Since I am not mechanically inclined I found this very helpful in understanding just what these ads were saying and NOT saying about an aircraft. BTW…LMNOP doesn’t mean a thing unless we use it for: Low Maintenance No Owner Present – many owners avoid keeping their plane current and legal.

Terms for Hours and Overhaul Alphabet soup!

Below are terms used in aircraft-for-sale advertisements showing the engine hours since the last overhaul were carried out are quoted. Hopefully this information will clarify what some of these terms mean and why it’s important not to confuse them.


Overhaul is a term used by the general aviation industry when an aircraft engine is cleaned, carefully inspected, and repaired or has parts replaced to meet service limits.

An overhaul is an overhaul as per the manufacturers specifications. There is no such thing as a major overhaul, just an overhaul, even though you will see the word “major” used to describe them.

Most overhaul’s are defined by the manufacturer with supporting documentation (usually Service Bulletins) that define what must be done and what parts must be replaced.

If an engine, for example, is advertised as overhauled, you have the right to ask how it was done. Was it done to factory new standards or to factory serviceable standards?

Only the very lower quality overhauls are done to factory servicable standards. It implies that many parts are reused instead of being replaced. This also applies to other components such as magnetos, carbs etc.

TSOH (Time Since Over Haul)

Time Since Over Haul is the number of flight hours since an Overhaul was performed.

TBO or TBOH (Time Between Over Haul)

Time Between Overhauls, an engine manufacturer’s recommended overhaul interval in hours, a rough and not guaranteed guide to life expectancy of an engine before it will need overhaul.

SMOH or TSMOH (Since Major Over Haul)

Since the overhaul process requires the engine to be taken apart, it is typically an expensive process. The value of a used engine decreases if it is close to requiring an overhaul, so used engines (and aircraft) typically list their time since overhaul or TSOH.

STOH (Since Top Over Haul)

Top overhaul is a term used by the general aviation industry when all the cylinders on the engine are overhauled or replaced with new, possibly due to corrosion.

TTSN, TSN, TT (Total Time Since New) or AFTT (Air Frame Total Time)

Total Time Since New is usually an airframe time reference for the total number of flight hours on a used aircraft.

TTAF/E (Total Time Air Frame/Engine)

Total Time Airframe and Engine(s) is usually an airframe time reference for the total number of flight hours on a used aircraft.

SFRM or SFRMN (Since Factory Re-Manufactured)

References to the time since the engines were remanufactured.

Blue skies!!!

Looking to Buy a Plane? Do the Research!

The Research Road

I have taken a great deal of time in the last couple of years in examining aircraft ownership for myself. In this update I have outlined just some of the initial research steps involved in getting clarity before there is even a pre-buy inspection. I started down this road because I saw a 1969 Cessna 182 in VERY good condition and really wanted to KNOW WHAT I DIDN’T KNOW in order to sum up an aircraft which would NOT need an overhaul. The research starts out like this…

Use the N# to contact the FAA Registration office for records of ownership (registration) and maintenance. It is cheap ($10.00) and won’t take long to get.


Use the N# on the NTSB site to see if there is any accident history.


Use the N# to learn what year/model the aircraft is and who it is currently registered to.


Use the FAA free web site to download the Type Certificate Data Sheet (TCDS) for the plane.


Use the FAA free web site to obtain a list of Airworthiness Directives (AD) notes on the major components of the aircraft (aircraft, engine, prop, mags, carb or fuel injection, vacuum pump, prop governor, etc)  that are listed on the TCDS, when you review the maintenance records you MUST be able to SEE PROOF that the AD notes have been complied with. If there is no proof than they will have to be compiled with as per the AD note instructions.


Now you will need information from the owner (real – matter of fact – backed by logbook information).

  • When was the aircraft last annulled?
  • When was the aircraft last flown?
  • What are total times on aircraft, time since overhaul (TSOH) on engine, carb, prop and all accessories.

How is the aircraft equipped? (Garmin 430, auto pilot, turbo charger?  etc) Begin looking at industry publications to try and find aircraft prices that are comparably equipped and same time. Use the AOPA listing or other blue book type listings.


Liens and Title

In the first step we talked about contacting the FAA Registration office for records of ownership (registration) and maintenance. You may request a copy of the aircraft record on a CD for $10 on-line at to review the record for outstanding liens yourself. However, this is no guarantee that a lien will be shown on the CD that you buy, especially if it’s a new lien. Keep in mind that the Aircraft Registration Branch does not do lien searches. For additional piece of mind you should contact a private company to do the search for you.  Under “AC Form AFS-750-55, List of Title Search Companies” you can find a list of companies and law offices that provide lien searches for a fee.

List of Title Search Companies

If you have any further questions, please contact the Aircraft Registration Branch directly at 405-954-3116 or 866-762-9434.  There are Legal Instruments Examiners on duty from 7:30 a.m. to 3:30 p.m. CST to answer your questions.

Aircraft Renter’s Insurance: Don’t take off without it.

When I was a student pilot I did buy renters insurance for a little while, but sometimes I felt that flying was expensive enough so why add salt to the wound? The truth is that unless you have the FBO or Flying Club policy in your hand and you know for a fact that the premium is PAID and the policy is current and up-to-date, you are assuming too much risk. As 2012 approaches it might be time to re-think this behavior and opt for more protection. Here is some useful information from the AOPA Insurance site located at: http://www.aopaia.com

Aircraft Renter’s Insurance: Don’t take off without it.

This insurance is for your personal and non-commercial use of non-owned fixed wing, non-pressurized, land aircraft having a non-turbine single engine of 450 horsepower or less (including non-powered sailplanes) and capacity of no more than seven (7) total passengers and/or seats (1 pilot and 6 other passengers), and a standard, experimental, restricted, or light sport aircraft certificate, and not furnished to you for more than thirty (30) consecutive days. Multi-engine and rotor wing aircraft are not included in this coverage. For multi-engine and rotorwing nonowned coverage, please contact AOPA Insurance Agency at 1-800-622-2672.

Why should I buy a non-owned policy? My FBO tells me they have coverage.

FBO has coverage for them. Some FBO policies have provisions which will cover students and renters for liability coverage and provide a waiver of subrogation, but without seeing a copy of the policy you will never know what rights you have (if any) under the FBO’s policy. You are much better off having your own coverage.

What is non-owned liability coverage?

It is a liability insurance policy to protect you against claims arising from bodily injury and property damage for which you are legally liable, caused by an occurrence arising from your use of a non-owned aircraft. This coverage does not apply to the non-owned aircraft you have borrowed or rented. Physical Damage to your non-owned aircraft must be purchased.

I do not rent aircraft, but occasionally I borrow an aircraft from a close friend. I am named on their policy as an approved pilot, don’t I have coverage?

The policy is intended to cover the owner of the aircraft not the user of the aircraft. Depending on the policy and insurance company you may be held responsible to any damage you cause to the aircraft.

Will a non-owned policy provide coverage for a borrowed aircraft that doesn’t have insurance?

If you purchase physical damage to your non-owned aircraft coverage, the policy will provide you with liability coverage while using someone else’s aircraft. Your non-owned coverage is not a substitute for the aircraft owner buying their own coverage to protect their interests.

What type of aircraft am I permitted to use if I purchase a non-owned liability policy?

Non-owned coverage is for your personal and non-commercial use of non-owned fixed wing, non-pressurized, land aircraft having a non-turbine single engine of 450 horsepower or less (including non-powered sailplanes) and capacity of no more than seven (7) total passengers and/or seats (1 pilot and 6 other passengers), and a Standard, Experimental, Restricted or Light Aircraft Certificate, and not furnished to you for more than thirty (30) consecutive days.

Does the AOPA Insurance Agency offer any type of insurance for rotorcraft or multi-engine aircraft?

Non-owned coverage is available for multi-engine and rotorwing aircraft, however, it is not available through the website. Please call the AOPA Insurance Agency for more information about these products at 1-800-622-2672.

What limits of bodily injury and property damage liability should I carry?

There is no standard recommended amount of liability coverage you should carry. You need to consider factors such as your personal assets, earnings, whom you carry as passengers, and how much insurance you can afford or that is available. We recommend buying the most coverage you can reasonably afford and that is available.

What limits of aircraft damage liability should I carry?

For non-owned physical damage coverage, it depends on the value of the aircraft you typically rent and whether or not you want to fully be covered in the event of a total loss.

Does my immediate family or I have protection if we’re injured?

This policy covers bodily injury to others including immediate family, but does not include the named insured on the policy.

Is there a deductible on the aircraft damage liability coverage?

Non-owned coverage does not have a deductible.

What effect does pilot experience have on non-owned insurance premiums?

None. Premiums are based on the limits of coverage you select.

Who should purchase a non-owned policy?

Any pilot who rents or borrows someone else’s aircraft should purchase a non-owned policy. Even if you are receiving dual flight instruction and not acting as pilot in command in a non-owned aircraft, you may be held responsible for any damages or injuries arising from your negligence.

When should I purchase a non-owned policy?

We recommend you purchase a non-owned policy as soon as you start your flying lessons. You may be held legally liable for any losses that may occur.

Will a non-owned policy protect me if I use a non-owned aircraft for other than my own pleasure and business use?

No. Non-owned policies do not provide coverage if the non-owned aircraft is being used for or in connection with:

Aerial advertising, towing, photography or connection with; hunting, herding or spotting of animals of any kind, including birds and fish; patrol or surveillance of any kind, including powerlines, pipelines, traffic or fires; skydiving or parachuting; closed course racing; flights off-shore in support of fan off-shore business or operation; external transportation of persons or property, including wire stringing, or construction.

My employer allows me to rent aircraft to travel on company business, can you cover my employer on the non-owned policy?

Your employer may be added as an additional insured under the non-owned policy

What payment plans are available?

We require annual payment at the time the policy is bound. You can purchase your policy online at www.aopaia.com with a credit card or pay with a check with your application by mail or phone 1-800-622-2672.

What is the term of a non-owned policy?

One year.

If I have a non-owned policy and I later decide to purchase my own aircraft, can I cancel my non-owned policy?

Yes. We will cancel your non-own policy and transfer your credit to your owner policy.

Does your non-owned aircraft policy include “loss of use” coverage?

Yes. As a result of destruction to tangible property to others, loss of use is covered.

Does a non-owned policy provide coverage for losses in excess of the limits on our flying club’s policy?

This insurance is excess insurance. If there is other insurance available to you, it will apply first.

Does your policy have any exclusion against landing on a private grass strip?

NO. However, the policy does exclude coverage when the non-owned aircraft is operated into, on or from an area that is not designed, maintained and used as an airport except a landing due to a recorded emergency. This exclusion will not apply to a forced landing due to emergency flight conditions.

Can I fly outside the continental US?

The non-owned policy covers flights within the political boundaries of the United States of America, Mexico, Central America, Canada, the Islands of the West Indies (excluding Cuba), and while enroute between places therein.

I am a CFI – Why do I need a non-owned policy?

The Comprehensive CFI policy covers your negligence arising from your personal use of non-owned aircraft, covers your negligence while instructing in non-owned aircraft and provides coverage for claims that may arise out of your professional liability as a CFI. Although few have been sucessful in suing a CFI for their bodily injury or property damage arising from alleged negligent instruction the Comprehensive CFI policy provides you with defense coverage (legal fees) which can add up to hundreds of thousands of dollars.

I fly for the CAP – Does your policy cover this?

Yes – an endorsement can be added to the policy to cover CAP flights.

I am not interested in liability protection, can I only purchase the liability for aircraft physical damage option?

No – The company will only package the policy with liability for bodily injury, property damage and physical damage to non-owned aircraft. You may purchase liability for bodily injury and property damage only though.

My spouse is learning to fly as well, can I add him/her to my policy?

The non-owned policy covers only one individual, your spouse must buy their own policy to cover their use of non-owned aircraft.

How do I purchase coverage?

Visit Renters Insurance or call 1-800-622-2672.