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Three Valves And A Heat Exchanger: A Love Story

Comparison Between Aerospace Projects and Industrial Projects

I was recently catching up with a friend who has worked as a process engineer in the oil and gas industry, as well as in the industrial HVAC (heating, ventilation, and air conditioning) industry. We were discussing some of the recent projects we had been working on, and as she began to describe one of her most recent challenges I started to chuckle. She asked me why I had laughed, and I responded, “I find the difference between the timelines of our projects to be very entertaining.”

She had been describing a particularly complex (and antiquated) industrial environmental control system which she had been in charge of sorting out within 6 weeks. She was a little confused when I explained aerospace timelines are measured in years as opposed to weeks; it was her response that really got me thinking: “But your system is basically just 3 valves and a heat exchanger, right?” So why does it take so long to complete a program in aerospace?

As it is with most industries, the answer to this question is multi-faceted but all the lines of questioning (at least that I’ve come up with) point towards two core concepts which play a major role in the technical execution of a program.

The first concept is certification. Every aircraft system must undergo rigourous test campaigns to prove the system meets the design requirements and is safe to fly. These test campaigns are usually very extensive and require demonstration of every aspect of the system functionality along with analysis to prove the robustness of the system. Test campaigns are multi-layered constructs which cover the lowest level component assembly line acceptance test all the way through to aircraft system flight testing.

The level of rigour to which a system is tested depends on the safety assessment of that system. For example, e.g. a newly developed engine falls under much more test scrutiny than a newly developed in-flight entertainment system. The length and complexity of these test campaigns (not to mention preparing for the tests) are a driving factor behind the long timelines associated with aerospace programs, but what drives these test campaigns? Why do they have to be so long and in depth?

The short answer to that question is the second concept: the System Safety Assessment (SSA) and Failure Modes and Effects Analysis (FMEA). Aircraft systems are subject to federal (and international) regulations in order to safeguard the public who utilize these systems for transportation. The focus of most of these regulations is ensuring the fidelity of the aircraft and the safety of the passengers. The onus is on the aircraft manufacturers to provide evidence that the aircraft they are attempting to certify is safe to fly. This evidence is usually in the form of test reports (per above) but is guided by the FMEA and the SSA.

The SSA is a system level event which determines which portions of a system are safety critical, and the extent to which those systems can fail and still have the aircraft remain operational (even if the system is not). The FMEA is the document which provides the details to support the SSA and provide the precise mechanisms of failure, the precise rates of failure, and the system effects of failures and associated reconfiguration. The FMEA is critical to understanding how an aircraft can be operated safely. Unfortunately, gathering the data for failure rates to determine the aggregate effect of component and subsystem failures is a time-consuming task which needs to be supported by empirical or analytical evidence.


In my experience, these are the main reasons as to why I have spent so much time working with three valves and a heat exchanger. How does your experience match up? Do you agree? Disagree? Did I overlook something important you worked on? Share your thoughts and experiences in the comments!

Disclaimer: Any views or opinions presented in this blog post are solely those of the author and do not necessarily represent those of Aversan Inc.


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