Sylvie Willis
The flapper valve is a component of the fuel system in aircraft, and its inspection is an important safety measure. For Learjet 35/36 aircraft, there has been some confusion regarding the inspection requirements for outboard flapper valves. Initially, a 600-hour inspection was mandated, but subsequent updates and alternatives were introduced, leading to some uncertainty. This paragraph aims to introduce the topic and address the specific question of whether flapper valve inspection applies to the fuel tank of the Learjet 35.
| Characteristics | Values |
|---|---|
| Flapper Valve Inspection | 600-hour inspection in AD 95-25-03 superseded by AD 2005-16-09 |
| An Alternative Method of Compliance (AMOC) released on July 6, 2004 | |
| AD 2005-16-09 superseded AD 95-25-03 on September 13, 2005 | |
| Learjet decided to keep the 24-month inspection of the new (S-461) flapper valves |
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What You'll Learn
Learjet 35/36 outboard flapper valve inspection
There is a lot of confusion regarding the inspection of the outboard flapper valves on Learjet 35/36s. The 600-hour inspection in AD 95-25-03 superseded by AD 2005-16-09 was originally for all flapper valves. However, an Alternative Method of Compliance (AMOC) was released on July 6, 2004, stating that the inspection of the new (S-461) flappers was to be per the applicable maintenance manual.
Although there is no specific requirement to inspect flapper valves, Learjet decided to keep the 24-month inspection of the new (S-461) flapper valves because that is when other wing fuel inspections are performed. IRN M2812000, for the old flappers, is still governed by AD 95-25-03 superseded by AD 2005-16-09, requiring a 600-hour inspection. The B4 IRN (M2812000) only applies to old flapper valves, while the "Due at Other Intervals" (24-months) IRN (M2812003) only applies to new flapper valves.
The flapper valves on Learjet 35/36s permit fuel flow inward but restrict outward flow to prevent sudden shifts in the aircraft's lateral balance. This is an important function that helps to maintain the aircraft's stability during flight. Therefore, it is crucial to ensure that the flapper valves are in good condition and functioning properly through regular inspections and maintenance.
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AD 95-25-03 superseded by AD 2005-16-09
The Federal Aviation Administration (FAA) Airworthiness Directive (AD) 95-25-03, which applies to Honeywell (formerly AlliedSignal) fuel boost pumps with a certain part number and serial number combination, has been superseded by AD 2005-16-09.
AD 95-25-03 was issued to address the potential for failure of the flapper valve inside the fuel boost pump, which could lead to a loss of engine power or a possible in-flight fire. The AD required initial and repetitive inspections of the fuel boost pump and, depending on findings, replacement of the pump with a serviceable part.
AD 2005-16-09 was later issued to expand the scope of the AD to include additional part numbers and serial number combinations and to require replacement of the affected fuel boost pumps with new, improved parts. This AD also specified that certain inspections required by AD 95-25-03 were no longer necessary due to the improved design of the replacement parts.
Therefore, if your fuel tank is equipped with a Honeywell fuel boost pump with the part number and serial number combinations specified in AD 2005-16-09, you would need to refer to the requirements of this AD to determine the appropriate action. This may include replacing the existing fuel boost pump with a new, improved part and/or performing any applicable inspections as specified in the AD.
It is important to note that ADs are legally enforceable rules that must be complied with within the specified timeframes. Failure to comply with an AD can result in serious safety risks and may subject persons to civil penalties and enforcement actions. Therefore, it is always advisable to consult with a qualified aviation maintenance professional or the aircraft manufacturer for specific guidance on AD compliance.
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Alternative Method of Compliance (AMOC)
An Alternative Method of Compliance (AMOC) is a deviation from an Airworthiness Directive (AD) that is approved by the European Union Aviation Safety Agency (EASA). It is a different way to address an unsafe condition on products, parts, and appliances. An AMOC must provide the same level of safety as compliance with the original AD.
In the context of the Learjet 35/36 Outboard Flapper Valve, there was confusion and frustration related to the inspection of the flapper valves. The original AD 95-25-03 required a 600-hour inspection for all flapper valves. However, on July 6, 2004, an AMOC was released stating that the inspection of the new (S-461) flappers was to be per the applicable maintenance manual. This AMOC superseded the original AD, and it was no longer required to perform a 600-hour inspection on the new flapper valves.
The new flapper valves (S-461) are made of S-461 rubber and are installed per SB 35/36-28-14. The old flapper valves are governed by the original AD 95-25-03, which has been superseded by AD 2005-16-09, requiring the 600-hour inspection. The B4 IRN (M2812000) only applies to the old flapper valves, while the "Due at Other Intervals" (24-months) IRN (M2812003) only applies to the new flapper valves.
Although the AD 2005-16-09 does not specifically require a flapper valve inspection, Learjet decided to keep the 24-month inspection of the new (S-461) flapper valves in Chapter 5, "Due at Other Intervals (5-10-29)", as this is when other wing fuel inspections are performed. This decision was made to maintain the safety and integrity of the aircraft, even though the AMOC provided an alternative method of compliance.
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Repetitive inspections per AD 2005-16-09
The flapper valve is a critical component of your fuel system, and its proper functioning is essential to ensure the safety and efficiency of your aircraft. According to Airworthiness Directive (AD) 2005-16-09, repetitive inspections of the flapper valve are required for certain fuel tanks, including those installed on H-35 model helicopters.
This AD was issued by the Federal Aviation Administration (FAA) to address the issue of cracked or damaged flapper valves, which can lead to fuel leaks and potential fires. By conducting repetitive inspections, aircraft owners and operators can identify and address any issues with the flapper valve before they become more serious problems.
The AD applies to all H-35 model helicopters equipped with certain fuel tanks, as specified in the directive. It requires initial and repetitive inspections of the flapper valve to ensure that it is in good condition and free from any defects or damage. The specific inspection intervals and procedures are outlined in the AD, and it is important that they are followed closely to ensure compliance and maintain the airworthiness of the aircraft.
In addition to visual inspections, functional tests may also be required to ensure that the flapper valve is operating correctly. These tests typically involve monitoring the valve's operation during fuel flow to ensure that it opens and closes properly, providing an effective seal when closed and allowing unrestricted fuel flow when open. Any deviations or abnormalities observed during functional tests would necessitate further investigation and, if necessary, appropriate corrective actions.
It is important to note that the specific inspection procedures and compliance requirements outlined in AD 2005-16-09 may vary depending on the aircraft model, fuel tank configuration, and other factors. Aircraft owners and maintenance personnel should always refer to the official AD document and seek guidance from the aircraft manufacturer or relevant authorities when interpreting and complying with the directive's requirements. By adhering to these repetitive inspection protocols, operators of H-35 helicopters can ensure the ongoing safety and reliability of their fuel systems, mitigating the risks associated with faulty flapper valves.
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Learjet's 24-month inspection of S-461 flapper valves
There seems to be a lot of confusion regarding the inspection of outboard flapper valves on Learjet 35/36s. The 600-hour inspection in AD 95-25-03 was superseded by AD 2005-16-09, which stated that the inspection of new (S-461) flapper valves was to be per the applicable maintenance manual.
While there is no specific requirement to perform a flapper valve inspection, Learjet decided to keep the 24-month inspection of the new (S-461) flapper valves because that is when other wing fuel inspections are performed. This inspection is only applicable to new flapper valves and does not apply to old valves.
The new (S-461) flapper valves have no life limit, unlike the old flapper valves, which have a 5-year life limit. The IRN for the new flapper valves is M2812003, and it is listed under "Due at Other Intervals".
To summarise, the Learjets 24-month inspection of S-461 flapper valves is done concurrently with other wing fuel inspections. This inspection is not mandatory but is kept by Learjet to ensure the proper functioning of the new flapper valves.
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Frequently asked questions
The AD 95-25-03 is a 600-hour inspection in for all flapper valves.
On July 6, 2004, an AMOC was released, stating that the inspection of the new (S-461) flappers was to be per the applicable maintenance manual.
The AD 2005-16-09 superseded AD 95-25-03 on September 13, 2005, stating that for aircraft with the new flapper valves installed, the repetitive inspections required by paragraphs (f) and (i) of AD 2005-16-09 could be terminated.
