The issue of what is legal (in FAA terms) and approved (by manufacturers) puts maintainers in a sticky situation. On one hand, the FAA issues a supplemental type certificate (STC) allowing for products to deploy on aircraft, but the engine and/or aircraft manufacturer may not approve or recognize the STC as something permitted for use under the terms of their warranty. 

Whether an aircraft owner or operator chooses to use the alternate fuel or not is a matter of choice. The fuel has been approved by the FAA and is perfectly legal to use in the SR series aircraft. The dilemma for the maintainer arises upon returning a Cirrus aircraft to service even for something as routine as an oil change. 

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Consider this scenario. The pilot opted to refuel with G100UL or the aircraft arrived with G100UL in the tank. This alternate fuel is a drop-in replacement, so 100UL could have been added to 100LL already in the tank. Granted the maintenance action in this case did not involve fuel, but the maintainer is signing for the entire aircraft to be returned to service. If they sign the repair IAW OEM guidelines, this includes Service Advisories (including one that prohibits the use of G100UL fuel). Consequently if the aircraft is carrying G100UL, then this could be an issue because the aircraft is not being returned to service IAW this Cirrus SB.

Of course, as with any guideline, the issue of signing for an aircraft is subject to interpretation. I know mechanics that will only work on aircraft they have personal history with and do not want to return to service an inherited unrecognized maintenance action.

In the advisory (SA24-14) “Transition to Unleaded Fuel and Use of Non-Cirrus Approved Fuel in SR Series Aircraft” released June 18, Cirrus said it was committed to the industry’s transition to unleaded fuels, which is underscored by its collaboration with stakeholders such as the Aircraft Owners and Pilots Association (AOPA), General Aviation Manufacturers Association (GAMA), FAA, and Eliminate Aviation Gasoline Lead Emissions (EAGLE) industry initiative.

Aircraft and engine manufacturer’s are extremely risk averse. They historically do not recognize alternate methods of airworthiness, and this includes STCs, parts manufacturer approval (PMA) parts, and designated engineering representative (DER) repairs.

There is a commercial element to this since any aftermarket PMA part procured from a third party is a revenue lost for the OEM. It appears the reason for the SB in this specific case is Cirrus’ concern about the breakdown of a fuel tank sealant that was seen in an isolated (one) aircraft known to have been fueled with G100UL.

The company will need to vet this against other aircraft in the fleet to ascertain if the perceived breakdown is an isolated outlier related to the drop-in fuel, or if the dislodged fuel tank sealant was a manufacturing defect unrelated to the use of G100UL. 

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“While some aspects of the initial Cirrus testing of the GAMI G100UL fuel are encouraging, other areas, including materials compatibility, remain inconclusive,” the advisory said. “At this time, Cirrus does not approve the use of GAMI G100UL fuel in Cirrus SR Series airplanes. Per Continental and Lycoming, only approved fuels may be used for an engine to be covered by warranty.” 

According to the FAA, G100UL is safe to use, hence the STC approval. This took years of testing to clear the milestones. In fact GAMI uses the fuel in its company SR22..

According to GAMI, the fuel has undergone substantial testing and displayed no issues on other aircraft. The company also disputes Cirrus’ claim that using G100UL voids the warranties on engines supplied by Lycoming and Continental, however, the engine manufacturers have confirmed its use could affect warranty claims, according to AVweb. 

Tim Roehl, president of GAMI, indicated that his team is drafting a formal response to Cirrus Service Advisory SA24-14 to be posted on its website. Roehl also said that the sealant Cirrus references is not the polysulfide sealant more commonly used in the industry but a polythioether sealant. Roehl stated that G100UL has been in service since 2010 on one wing of the company’s Cirrus SR22, using the same polythioether sealant Cirrus uses, with zero incidents.

The FAA does not comment on specific OEM warranty policies but the agency has reiterated that GAMI’s G100UL does have the STC approval. This is not uncommon as the FAA routinely approves alternate solutions without the buy-in from OEMs. The burden is on the third-party solution provider to prove airworthiness—i.e. STC holder, PMA manufacturer, or designated engineering representative for DER repairs.

What This Means for Maintainers

This fuel issue places aircraft maintenance professionals in a bit of a quandary. On one side, you have the FAA approval for G100UL, but at least one aircraft manufacturer, Cirrus, and one engine manufacturer, say they are not approved via service advisories.

The FAA typically steers clear of airframe/powerplant OEM issues until they become an airworthiness directive (AD). To assist in clearing any confusion, the agency issues periodic documents to help owner/operator/maintainer stay abreast of the situation. One such publication is the FAASTeam service bulletins.

When asked if service bulletins are mandatory, the FAA says: It depends. 

Here is a quick agency ruling: “If you are operating your aircraft under 14 CFR part 91, a service bulletin is advisory, and compliance is not mandatory unless it is included in an Airworthiness Directive.”

Another resource is FAA Advisory Circular AC 20-114, which addresses manufacturers’ service documents: “Service documents should be neither treated nor represented as the official FAA approval documents, unless either a letter of design approval from the FAA or a record that compliance has been determined by an FAA designee is on file for recommended actions indicated as FAA-approved in service documents.”

That said, service documents are beneficial and transmit a wealth of knowledge. When returning aircraft to service, it is critical to list if the action is in accordance with OEM information or another alternate form of maintenance. This comes into play when installing PMA parts, or an STC like G100UL.

The post Cirrus Service Advisory Throws Fuel on G100UL Maintenance Debate appeared first on FLYING Magazine.

According to a report issued on April 12 by the NTSB, the six accidents were the result of excessive fuel flow in the SR22T, which caused engine failure during climb out. The accidents, which happened between 2017 and 2019, resulted in three deaths and nine persons injured. 

During the accident investigations, the NTSB removed the recoverable data monitors from the accident aircraft and determined that in each case the aircraft indicated an excessively high fuel flow rate, ranging from 42.2 to 50.1 gallons per hour, just before the engine lost power. 

According to the Cirrus pilot’s operating handbook for the SR22T, the electric fuel boost pump has two activation settings: 

• “Boost,” which should be used for takeoff, climbout, and when switching fuel tanks
• “High Boost/Prime,” which should be used for engine start and to avoid vapor lock above 18,000 feet. 

According to information from Cirrus, when the pump is in the “Boost” mode, it can deliver 19 gph. In the “High Boost/Prime” position, the electric fuel pump can deliver 42 gph. 

The NTSB report stated that in two of the accidents, the pilot had incorrectly selected the “High Boost/Prime” mode, resulting in the excessive fuel pushed to the engine. The excessive fuel overloads the engine, similarly to the way chugging a beverage makes a person choke.

A third investigation determined that an improperly adjusted slope controller and fuel pump were to blame for the loss of engine power.

Cirrus Takes Steps to Mitigate Risk

In May 2018, Cirrus issued service advisory (SA18-02) for the SR22T, reminding pilots that the intended use of the “High Boost/Prime” function, per the POH, is only used for engine start and suppressing vapor lock in flight above 18,000 feet with warm or hot fuel.

The SA continues: “The fuel pump should be set to ‘Boost’ for takeoff, climb, landing and when switching fuel tanks, and that the fuel flow should never exceed 41 gallons per hour at 36.5 inches of manifold pressure, as higher fuel flow rates may result in a rough running engine or loss of power.”

In addition, Cirrus implemented software changes to prevent improper use of the electric fuel boost pump on the SR22T, which features Garmin’s Perspective or Perspective Plus avionics suite.

Pilots and aircraft owners were notified of the software change in a service bulletin on a controlled lockout feature for in-service SR22Ts. 

The lockout feature was designed to block the use of the “High Boost/Prime” function until the airplane reaches a pressure altitude of 10,000 feet to prevent a loss of engine power at low altitude.

However, Cirrus received pilot reports that the lockout function was not operating as intended, and in January 2019 Cirrus issue Service Advisory SA19-01 stating “Use of HIGH BOOST/PRIME fuel pump mode in flight below 10,000 feet is not recommended and should be avoided” and “until a software update is released to address this condition, the use of HIGH BOOST/PRIME fuel pump mode should only be required in flight above 18,000 feet on hot days with warm of hot fuel to maintain fuel flow in the green arc or to suppress vapor formation.”

FLYING reached out to Garmin for comment on the issue, but our request for information was not immediately returned.

NTSB Recommendations

The NTSB recommends that Cirrus conduct an functional hazard assessment to identify the causes, effect and severity levels for the SR22T during takeoff and climb phases of flight, and to use this information to identify mitigating actions such as design modifications or changes in procedures for the operators of the aircraft.

In addition, the NTSB is asking the FAA to require implementation of proper mitigating actions to prevent power loss during excessive fuel flow and that the FAA review the FHA recommendations made by Cirrus.

Cirrus Aircraft issued a statement responding to the NTSB report, noting that because the investigation is active: “Cirrus Aircraft cannot comment on the particulars of the aircraft incidents or participate in any speculation as to the cause or the explanations for fuel flow in each case. 

“Cirrus Aircraft personnel are fully supporting these investigation activities,” the statement continued. “Cirrus Aircraft has shown that all configurations of the Model SR22T and its Continental TSIO-550-K engine are compliant with 14 CFR Part 23 and meet all applicable safety standards. All SR22T aircraft manufactured by Cirrus Aircraft meet all airworthiness requirements when they receive their original airworthiness certificate. Any SR22T that is operated in accordance with the approved Pilot Operating Handbook and has been maintained in accordance with the Cirrus Airplane Maintenance Manual will continue to meet all airworthiness requirements with no unsafe conditions.”

The post NTSB to Cirrus: Address Fuel Boost Pump Issues with SR22T appeared first on FLYING Magazine.