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Avoid the hidden engine costs before you buy

When purchasing an aircraft- it is easy to take for granted that the condition of the engines are as advertised- if they all meet the parameters specified by the engine manufacturer.

Adopting this laissez-faire approach to the engines that are mounted on your prospective purchase aircraft- may come back to haunt you with some very costly hidden deficiencies. I shall elaborate…

Having passed through what appeared to be a thorough pre-purchase inspection- the buyer and seller of a Canadair Challenger CL600 shook hands via fax machine and the transaction closed. The new owner was very pleased with his purchase- and promptly scheduled multiple flights on the aircraft until the end of that year. He knew that both his pilot and maintenance facility had performed the pre-purchase inspection for him- and both had confirmed one of the engines was coming due for an overhaul at about the time when he had planned for his flying to stop- just before Christmas.

The purchase price had been commensurate with this pending event and the removal of the engine and shipping to an overhaul facility had all been arranged in advance. All this would coincide with a regular airframe inspection.

By the end of January the engine was ready for shipment and reinstallation on the aircraft- and all that was needed was full payment of the overhaul to be made prior to shipment.

What caught the new owner’s attention was the fact that he was faced with an invoice of more than $200-000- when his understanding was that both engines were covered 100% by an aftermarket engine maintenance support contract. As far as he was aware- there should not have been a single cent owed by him!

What none of the advisors employed by the owner managed to report to him was the specific definition of what 100% meant contractually- and what was specifically covered by the program. After the owner had taken the time to read the contract himself- he quickly learned that the parts and labour to perform the Overhaul were all picked-up by the service plan provider- but the replacement of all of the lifelimited components that were due for replacement at this event- were only pro-rated by the smaller amounts that had been accumulated against them by the previous owner’s chosen payment plan.

This plan had been transferred to the new owner at the time of purchase. Nobody was injured- and nothing was damaged by this basic mistake; however both the new owner’s pride and wallet took a beating here because he had not foreseen this hidden expense.

Unfortunately there are similar examples of hidden engine problems that have actually led to property damage- and in some awful cases- loss of life.

 

Corrosion and the Environment
Most engine manufacturers have some form of corrosion detection program written into their maintenance schedule. Most people are concerned with the normal wear and erosion that takes place over the service life of an engine between hot sections and overhauls. Few think of corrosion as a factor in their inspection cycles- mainly because modern alloys and their exotic coatings have managed to eliminate many of the problems found in early turbine engines.

Various forms of corrosion can still cause significant hidden damage even on engines that are used almost daily. The geographic location of where the aircraft is kept and flown is often the key. Salt water will readily eat away at aluminium alloys and highly stressed steel components; while silica dust (sand) will strip protective coatings from cases and blades with ease.

There are maintenance strategies that can be employed by the owner’s maintenance people that are designed to minimize the effects of these harsh environments. This should not become a problem for a buyer- as long as these strategies (frequent compressor washes- for example)- have been performed and recorded in the maintenance records. If not- then buyers beware!

Several aircraft engine manufacturers in the turbine and piston engine categories have published recommendations for early overhauls- or at the very least- tear-down inspections that are based upon a calendar limit (usually a 10 to 12 year cycle)- independent from the normal hour and cycle limits. Unfortunately many owner operators choose to interpret the rules of the governing authority that oversees their flight operations- and believe that these recommended limits simply don’t apply to them. Again- buyers beware!

 

The Soap Test
Whenever we humans start misfiring and getting wobbly- our doctors will usually arrange for various blood tests to be performed- enabling an accurate diagnosis to be made. If we had the wherewithal- most of us would probably choose to have a regular blood testing program installed- so that anything untoward in our health would be caught before any physical symptoms were experienced. Unfortunately the majority of us don’t have such a program available to us- until it is almost too late.

Fortunately there is such a program that is relatively inexpensive available for all aircraft engines and airframe hydraulic systems. This program is called the Spectral Oil Analysis Program (SOAP).

If your target aircraft is not currently enrolled in this type of widely available program- then at the absolute minimum- require that SOAP samples be taken during a pre-purchase inspection- and don’t close until the results have been returned from the laboratory. How a SOAP test works is that when the oil samples sent for testing arrive- they are documented and then placed into a thermal mass spectrometer.

The modern units are highly automated and computerized. Their function is to effectively heat the oil sample sufficiently to chemically break the sample down into its component parts- which can then be analyzed for all trace materials- including engine or systems metals that should not be present. When complete all findings are compared to the master engine profiles held by the laboratory and then a report is issued with the findings annotated.

The SOAP test has proven to be extremely effective at providing early warning detection of irregular wear or malfunction within engines and other systems. If a SOAP test is not included in a pre-purchase inspection- then I say again; buyers beware!

 

Borescopic Inspections
The only truly effective way of making sure that the internal condition of the engines that are installed the aircraft you’re buying is normal and serviceable is to require a tear down inspection during the pre-purchase inspection. Sadly this is not often allowed. The next option open to you is a borescopic inspection.

A borescopic inspection entails a miniature flexible fibre-optic viewing tube being inserted sequentially through various openings throughout the engine structure- with the actual close-quarters image being optically viewed either through an eyepiece or on a monitor. This method of inspection is not as effective as a teardown inspection- but at least the diagnosis from the images viewed and analyzed by an experienced inspector- can be more than 95% effective in finding hidden defects- like corrosion- erosion- wear- burning- cracking- deformation and/or foreign object damage (FOD).

A less than 5% risk factor is certainly better than a 100% risk factor - therefore buyers beware if a borescope inspection method isn’t included in a pre-purchase inspection.

 

The ‘Pre’- Pre -Purchase Test Flight
Another valuable tool employed by an aircraft purchaser prior to pulling the trigger on an aircraft purchase closing- is the ‘pre’-pre-purchase inspection test flight - the ground running of engines to determine that their performance is matching the manufacturers’ specified parameters is okay. This certainly should be an important item on a pre-purchase inspection workscope- but unfortunately it may also fail to tell the whole story.

Whenever it is possible to negotiate two test flights into your purchase contract- I strongly recommend that you try to do so. In fact if the aircraft has to be positioned to a pre-purchase inspection facility that is at least forty five minutes away- this is an ideal time to do the test flight.

But before your inspector leaves the ground in the aircraft- a written flight-test plan should be agreed upon by both parties.

Failing this- arrange for the delivery crew to stick around after arrival at the pre-purchase facility- and then have several of the pre-purchase facilities’ lead inspectors (engine- systems- avionics- and interiors) to hop aboard and go out on a thorough hour-long test flight. What you will achieve with this test flight is to get a first hand account of the operational performance of the aircraft in flight including:

• Fuel-flows - for various power settings and altitudes;
• Temperatures (EGT/ITT/Oil);
• Speeds (Fan N1/Turbine N2) and;
• Pressures (EPR and Oil)- etc.

Additionally when an aircraft is in cruise at altitude- the airframe will cold soak and structurally its dimensions will alter very slightly. It is better to learn that the lavatory door sticks at altitude- but works fine on the ground- or that the cabin pressurization system bumps the cabin on rotation- hurting your ears now- before the pre-purchase inspection starts in the hangar. Imagine if you only find these deficiencies out on your first trip with your best customer’s wife aboard.

Finally- during the descent for landing- make sure that the approach is flown coupled by the autopilot. This will hopefully make any irregularities or deficiencies within the automatic flight control systems show up- which is something that is nearly impossible to do on the ground with a test box. Even today’s all-digital- all-computerized aircraft may still hide some demons that will not be seen until you are airborne.

 

The Five-Point Run (JEDA)
Most pre-purchase inspections include an engine ground running procedure. The agency working on your behalf will perform regular tests- including loading the aircraft up with fuel- checking the wind direction- speed and temperature- and then going out and running the engines with the aircraft angled for a crosswind- while referencing the parameter graphs from the maintenance manual for the aircraft. However- I strongly recommend you commission a complete external instrumented multiple data-point run with vibration survey (often referred to as a five-point run or JEDA) be performed too.

If the agency that is working for you doesn’t have the necessary equipment to accomplish this- request that it hires an independent contractor to come in and do it for them.

For those not familiar with the five-point run operation- effectively two or more separate certified (recently calibrated units) will be hooked-up by various leads to all of the following points: Fuel Flow- Temperatures (ITT- PLA- TT2 and OAT)- Speeds (N1 and N2)- Pressure (PT2)- and a bolt-on Fan vibration accelerometer. This is a vital component of a thorough prepurchase inspection because it isolates all of the on-board gauges instead of just relying on their displays.

Often when I have been in charge of an aircraft acquisition project- and I specify that a complete JEDA run be performed- many deficiencies are found. The biggest problem that is usually found during the JEDA run is that the onboard instruments are way out of calibration- and the engines have been either required to under- or over-perform. It can be assumed you will agree that this is a dangerous situation in both instances. Again- buyers beware!

 

Limited Cycle Fatigue (LCF) Components 
The last area of concern in this feature is that of Limited Cycle Fatigue (LCF) Life Limited Components. This- essentially- is where certain major components within an aircraft turbine engine are deemed by the manufacturer to have a limited life-span before they are to be withdrawn from further service and scrapped. This life-span limit is usually counted in engine cycles (one cycle = one flight).

Unfortunately operators often fail to read the engine maintenance manual where they’ll find scenarios explained where exceptions to the one cycle per flight rule count. Usually these exceptions cover certain unusual operations like the use of high-power settings for an extended period- operation above certain temperature limits and even multiple touch-andgo flight operations.

The components most likely to be cycle-lifelimited are all of the compressor and turbine disks- blades and stators (sometimes)- shafts and occasionally the seals. These components are the most highly stressed components within an engine and if they failed- their failure would most likely result in the destruction and/or complete failure of the engine. They are also usually very costly to replace when their limit is reached. Fortunately the LCF components usually have a considerable life span in the tens-of-thousands-range which is economically the better.

Unfortunately- often the lives of many LCF components don’t equate to an even number of the required Overhaul/engine tear-down events throughout the normal life of the engine. This is where accurate engine service records- and a seriously competent log book audit is absolutely vital when a pre-purchase inspection is performed. Drawing from the first real-world example of a hidden cost event (the proud new owner of a Canadair Challenger CL600 at the start of our article)- you can see why this issue becomes so important.

To draw on a second example- a Cessna Citation 500 was departing from an airport at Salt Lake City in 1996. During its take-off roll with throttles fully advanced- one of its engines (a JT15D) exploded- showering the aircraft and runway with metal shrapnel. Fortunately the aircraft and its occupants never left the ground- and therefore no-one was injured or killed.

What the NTSB later found to be the cause after investigation- was that this engine experienced an ‘uncontained engine failure’ (parts flew out of it- through the cowlings and other containment structure) due to the Rupture of the Fan Impeller Disk. This aircraft had spent several years outside of the US in the hands of a foreign operator- whom it appears did not keep suitable engine records. Thus it is assumed that the catastrophic failure of the Impeller was due to its life being exceeded. Yet again- buyers beware!

 

Buyers Beware Reference List
The following are some of the hidden cost items that I have personally experienced on various aircraft that I have bought and sold at JetBrokers- Inc. This list is not conclusive- but at least it may give you sufficient concern to give the engines the thorough inspection that they deserve before you buy a pre-owned aircraft for sale.

• For engines that have been approved to operate outside of the manufacturer’s specified operating service limits- under the auspices of an FAA Approved Aircraft Inspection Program (AAIP)- I have specifically had issues with main engine shaft bearings.
• Engines that have excessive gearbox pressures- which was usually due to worn- or failed bearings- or seals.
• Engines that have excessive vibration due to fan rotor imbalance- FOD- or wear.
• Faulty engine gauges- either under- or over-reading.
• Missing log books or individual maintenance event entries.
• Engines that have not been modified by required service bulletins or airworthiness directives.
• Engine accessories (fuel control units- fuel or hydraulic pumps- overspeed governors- etc.) that have been over looked at an overhaul- and are therefore either failed- or way outside of their operating service life.
• LCF components that won’t make it to the engine’s next schedule Overhaul or teardown inspection.
• Cracked- burnt or streaking fuel nozzles (these issues can kill an engine dead within minutes- if not caught).
• Corrosion- especially within engine compressor sections.
• Burnt- cracked or missing compressor or turbine blades/stator

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