The Tornado Alley Turbo Normalizing system adds additional utility and performance to an already great aircraft. Whether it is a system that was factory installed at Cirrus during production or an aftermarket kit obtained directly from TATI (Tornado Alley Turbo, Inc.) it is a feature that can make your aircraft climb faster, fly higher and get you to your destination quicker. However, as these systems are beginning to age there are some issues emerging that as an owner and pilot you should be aware of to help maintain your aircraft at optimal safety and performance levels.
TATI has several service bulletins and instructions that are important to perform on a regular basis but it has been my experience that on some aircraft these service documents are being neglected which could lead to expensive and potentially dangerous component failures. With this article, I am going to detail some of the most common service difficulties I have seen with the system, discuss two of the most important service instructions that TATI has published and present examples of why you should be making sure that your system is being inspected and maintained regularly.
The most common difficulty with the turbo normalizing system seems to be the heat shields. While they may seem a relatively harmless component, they could cause damage to some expensive parts of the system if they are ignored. During routine maintenance, the heat shields should be checked for condition and security of the clamps and to ensure that the edges of the heat shields do not come into contact with the exhaust pipes. There are two failures that I often see. The first is cracking of the heat shields either in the heat shield itself or the mounting foot that secures it to the exhaust tube. Unless you have a welding shop that can provide top notch repairs, replace any cracked or damaged heat shields for they are really not all that expensive and the replacement could be an upgraded design which would improve it’s durability.
Second, it is common for the band clamps that secure the heat shields to be found loose when an aircraft arrives for maintenance. Loose band clamps allows the heat shields to move out of position and cause problems. Just tightening them again is not usually sufficient to secure them until the next maintenance event as the clamps are likely damaged in some manner. Either the slots in the band are distorted or the tensioning screw is loose/misaligned in it’s housing. If the clamps are damaged in any way or difficult to turn I would recommend replacing them.
Loose heat shields can cause damage in a couple of ways. The edges of the shields can chafe against the exhaust manifolds, wearing into the material to the point where the manifold tube is rendered unserviceable. A loose heat shield can also contact and wear into the cylinder drain lines potentially allowing fuel to leak into the engine compartment and possibly onto hot exhaust components.
Slave Waste Gate
The second most common difficulty is with the slave (right) waste gate. The original design of the system incorporated a rod traveling across the back of the engine that connected the master and slave waste gates together. This design vibrated excessively and caused a high rate of wear on the components, especially the clevis pin that connected the rod to the slave waste gate. An improved design was soon introduced that replaced the rod with a cable control system that incorporated a spring to keep tension on the cable. Most aircraft with the older rod design have since been retrofitted with the newer design.
The cable control system resulted in a reduced wear rate, however it did not eliminate it completely. There is still wear occurring at the slave waste gate which could compromise the integrity of the components. Most of the wear occurs to the clevis pin and if it fails it will shear in half and you will lose control of the slave waste gate completely. The clevis on the control cable and the arm that controls the waste gate could also have excessive wear which might inhibit proper movement of the waste gate as the controller commands changes in the amount of boost required. Additionally, I have noticed that some waste gates are showing excessive exhaust leakage past the top bearing, possibly because the spring and cable system does not hold the control arm rigidly in position and it might be oscillating rapidly as the engine is running causing increased wear.
My recommendation is to have the slave waste gate inspected every time your aircraft is in for an oil change. Regardless of condition, replace the clevis pin at each maintenance event so that any movement between components is minimized. While not a perfect solution, doing so could help reduce the amount of wear that is occurring to the more expensive components. Since we have just started that practice at our facility, not enough time has been put on the turbo normalized aircraft that we service to see if it will make a difference but I am hopeful it will.
Exhaust Manifold Slip Joints
The third area of concern covers the exhaust manifolds, especially the slip joints. TATI has a service instruction, SI11-01, that covers the inspection of the slip joints to ensure that they exhibit movement between the components. It also details a tear down, inspection and cleaning of the exhaust manifolds and lubrication of the slip joints with a special anti-seize during reassembly. After finding several examples of damage caused by frozen slip joints I consider it critical that all owners of turbo normalized aircraft follow the instructions contained in SI11-01. In addition, at every oil change I strongly suggest that the heat shields be removed and the slip joints inspected to ensure they are moving correctly and to detect any swelling or cracking of the exhaust manifold tubes on either side of the slip joints. Have your technician pay particular attention to the slip joint between cylinders 2 & 4. I have seen four examples of blistering & cracking and one complete failure resulting in a crack all the way around the tube with a 1/8 inch gap between the pieces at this slip joint. In all cases, the damage started underneath the heat shields which is why I recommend removing them for the inspection. If the heat shields are left in place, any damage that could potentially exist would remain hidden until it had advanced around the tube possibly resulting in a breach and hot exhaust gasses flooding into the cowling.
If it is suspected that a slip joint may not be moving correctly perform the inspection and cleaning part of the service instruction. I also recommend performing the tear down cleaning at the recommended V-band replacement interval as suggested in SI11-01 but no longer than 500 hours. We have found the slip joints beginning to freeze up at 500 hours and they can be difficult to disassemble without damaging the exhaust components. It is an estimated 8-10 hours of labor to accomplish the cleaning plus miscellaneous parts but making sure the maintenance is performed on a routine basis could prevent you from having a very bad day in the air.
There are other important service instructions that could be performed concurrently with SI11-01 because the same components will have to be removed and disassembled to accomplish them. Doing all the service bulletins at once will ensure that other components are in good operating condition while cutting down on labor costs.
Engine Driven Fuel Pump
The fourth area of concern is the engine driven fuel pump and SB11-02. It has been found that some fuel pumps can leak fuel past the seals on the mixture control shaft. Inspection of the fuel pump using the instructions contained in SB11-02 should be performed every time the cowling is removed. Especially during an oil change because the removal of the oil filter gives good access to the pump and great visibility. Inspection only takes a couple of technicians a few seconds to perform. If the fuel pump is found to be leaking and your engine is within the terms of the Platinum warranty, Cirrus will cover replacement of the pump, parts only. Labor costs are the responsibility of the owner. If out of warranty, TATI will repair your pump for a relatively inexpensive cost compared to the price of an overhaul.
Do not neglect this service bulletin. I have seen five engine driven fuel pumps leaking so far with two examples where fuel was flowing steadily out of the mixture control shaft seals and running down the back of the engine when the electric pump was operated.
With the fuel pump shown above, I am sure that fuel was also leaking with just the engine driven pump in operation while the aircraft was in flight. Fuel stains were evident on the cowl and belly. Between inspections by your maintenance facility, I suggest that during your pre-flight you make it a habit to look for any signs of fuel stains in the lower cowl vents or unusual streaks trailing down the belly of the aircraft. If you see any suspect stains at all have the fuel pump inspected before starting the engine. This could well be another “very bad day” item if it is not detected and corrected.
Previous Generation Tail Pipes
A fifth concern primarily applies to aircraft equipped with older tail pipe designs. Either the original “S” shaped pipes or the straight pipes with flat side cabin heat exchanges welded onto them. These pipes are prone to cracking around the heat exchangers. An example of one that cracked all the way around and separated into two pieces was recently discovered at our facility when the cowling was removed for an unrelated issue. Inspect these exhaust pipes carefully for cracks and perform a pressure check of the heat exchangers regularly.
I have seen several of these pipes that have cracked and were repaired by welding. I would strongly recommend that these tail pipes not be repaired if they are found cracked. If you have a cracked tail pipe welded, the next time it cracks it might travel into the heat exchanger and you could end up breathing exhaust gasses. Your safest route would be to scrap it and upgrade to a new tail pipe. The most current design with rounded heat exchangers is more robust and I have yet to see one of those fail. Note: If your aircraft is equipped with an early turbo normalizing system, a few changes might need to be performed if upgrading to the new tail pipes. The cabin heat hose diameters were enlarged in later designs and the engine breather hose was relocated to an outlet on the left tail pipe. Keep that in mind and have your technician speak with a TATI representative to ensure you get the adapters you need for your aircraft when ordering parts.
The five items I discussed in this blog are just a part of inspecting and maintaining your Tornado Alley Turbo Normalizing System. Routine maintenance and replacement of time limited components as recommended by TATI in the Continued Airworthiness Manual and supporting service bulletins is good operating practice and can catch potential problems before they become serious.
The service bulletins mentioned and other important service information such as the Continued Airworthiness Manual are located on the TATI website at http://www.taturbo.com/drawings/. Make sure that your technician is aware of this resource and use the information contained therein to ensure that the integrity of your turbo normalizing system is maintained at the highest level. Doing so will mean that your aircraft will continue to be reliable and, most importantly, safe every time you need to fly.
Director of Maintenance
Platinum Aviation Service