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How to Verify and Troubleshoot Bleed Air Leaks

What can you do to establish whether you have a leak in your aircraft's bleed air system? Having detected one, how can you determine the cause? Duncan Aviation's Brad Wales offers suggestions.

Brad Wales   |   22nd January 2020
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Brad Wales Brad Wales

Brad Wales is Duncan Aviation’s Assistant Engine Line Manager. He oversees and manages daily...
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Inherent to most aircraft is the need to utilize engine bleed air. So, when leaks in the bleed air system occur it’s best not to ignore them. While a leak won’t fix itself, there are steps you can take to verify and troubleshoot one. Duncan Aviation's Brad Wales shares how...
 
A bleed air leak is a common discrepancy that has the potential to be very detrimental to engine performance. Yet, they are often solved with a simple fix.
 
Let’s first establish how engine bleed air works. Typically, bleed air is taken from two locations off of the engine compressor:
 
  • Low Pressure (LP) bleed air is taken from the Low Pressure Compressor (LPC)
  • High Pressure (HP) bleed air is taken from the High Pressure Compressor (HPC).
There are many uses for bleed air, including environmental control systems, pressure regulating, fuel/hydraulic, starting and ice protection systems. Bleed air leaks can be detected when you download trend data, or through engine trend monitoring services. They are commonly identified from an increase in Interstage Turbine Temperature (ITT), with little changes in N1 or N2 indication.
 
Verifying Basic Bleed Air Leaks

Bleed air leaks get blamed for many engine discrepancies (such as engine degradation). Before you take any troubleshooting steps, you should verify that a bleed air leak is indeed the culprit.
 
At the first sign of any bleed air issue, verify the engine indication systems.
 
You may think you’re experiencing engine performance degradation, when actually the problem may be may be an engine indication discrepancy (such as a faulty sensor, probe or harness).
 
It’s always good practice to compare engine trend data among all aircraft engines before troubleshooting. Often a crew reports that one engine is running cooler than the other, leading technicians to troubleshoot an engine that is operating within normal parameters (instead of isolating the hotter engine and the actual problem).
 
Troubleshooting Bleed Air Leaks
 
If a bleed leak is determined to be the actual cause, remove the engine cowlings and perform ground run leak checks.
 
You should always consult the OEM’s Fault Isolation Manual. Many engine models are capable of isolating bleed leaks by blocking off engine LP and HP ports and performing engine performance runs.
 
Identify and inspect all components in the system, because the problem could be as simple as a degraded gasket or seal (some seals and gaskets can become brittle and crack over time).
 
Check the functionality of your engine bleed air valves. The bleed air valves prevent compressor stall/surge during engine operation.
 
This may require a bleed off valve check/surge valve check, per the OEM’s direction, or a borescope inspection of the valve(s).
 
Be aware that the bleed valve can become stuck in a particular position, in which case, the following should be noted:
 
  • If stuck in the open position, there is a severe engine performance indication.
  • If stuck in the closed position, there are issues with associated aircraft systems.
  • If stuck in a transient position, you may see a failure in performance and failure in the associated aircraft systems.
Above all else, always reference the OEM Maintenance Manuals for engine troubleshooting and repair, since engine and aircraft make and models vary with the operation.
 
More information from www.duncanaviation.aero
 

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