ArticleThis article, written by our materials science practice, discusses a few case studies involving jet engine failure and what went wrong to cause it.
It is an unfortunate reality that planes crash every day.
From large commercial airliners to small private jets, there is a complex interplay between an extensive list of factors, any one of which can result in catastrophic failure. Aircraft design methodologies are founded on removing high-risk components and maintaining a comprehensive usage history; however, manufacturing errors, design errors, material defects and corrosion all remain common causes of failure in aircraft engine components. A few case studies are described here involving jet engine failure and what went wrong to cause it.
Turbine Disk Failure
In metallurgy, fatigue is the weakening of a material from iterative applied loads. The iterative load applied to turbine disks is primarily experienced during climb and reverse thrust. These processes repeatedly subject engine materials to extreme temperatures and pressures.
Aircraft design methods have shifted from safe-life, where parts are used for a fixed amount of time then retired, to a damage-tolerant design, where parts are used indefinitely so long as they remain within acceptable damage tolerances. The damage-tolerant methodology is more heavily dependent upon inspection, which brings in a human component, relying on inspectors to determine, e.g., if a crack in a turbine disk exceeds a critical length to the point where the part must be replaced.
Qantas Flight 32 on November 4, 2010 experienced engine failure in a Rolls-Royce jet engine on an Airbus A380, the largest passenger plane in the world, which required the plane to make an emergency landing. None of the passengers or crew were injured, but the engine and collateral debris caused structural damage when it fell from the air and crashed into buildings. The cause of the failure was determined to be fatigue cracking from misaligned sub-engine parts. This manufacturing defect resulted in oil leakage that became ignited, causing the failure. The lot of Rolls-Royce engines that were believed to be susceptible were inspected, many of which were subsequently removed from service.
It should come as no surprise that airplanes are designed with stringent specifications; the utmost of which are engine parts, which are constantly subjected to an extreme environment consisting of rotating parts at high temperatures and pressures. When parts are interchanged throughout a plane’s life, it must be ensured that, if a part is used that is not a direct replacement for the original, all materials, design and processing specifications result in a component that is airworthy.
On July 29, 2006 a plane chartered for skydiving experienced jet engine failure and crashed. Tragically, there were no survivors. The failure was attributed to aftermarket replacement parts. The aircraft was originally equipped with Pratt & Whitney jet engines, specifically made with pack-aluminide coated turbine blades to prevent oxidation of the base metal. However, during the plane’s lifetime, the turbine blades were replaced with different blades that had a different coating and base metal. As a result of the replaced turbine blade not meeting specification, it corroded, cracked and caused engine failure. The claims were settled for $52.5 million.
When any civil aviation accident occurs, the NTSB is charged with investigating the incident. These investigations commonly draw on for years. During that time, the involved parties must cooperate with the probe, which can hangar fleets for long periods of time. The sudden grounding of many aircrafts is felt across various parties in the aviation industry. The manufacturer immediately faces challenges with recouping investments. The carriers, who have the aircraft in service, also feel the economic fallout. All this does not even include the cost associated with fixing the problem once it is discovered.
On October 15, 2013 a Spirit Airlines Airbus A319 plane experienced in-flight engine failure and had to make an emergency landing. The event provoked the NTSB to launch an investigation. Immediately, Spirit Airlines began significantly delaying flights to perform inspections on its 51 plane Airbus fleet. Conservatively, Spirit expects $10 million in costs associated with this engine failure. This is all before the root cause of the problem has been determined.
Our experts in materials science and failure analysis are frequently retained when the consequences are dire. Our experts typically perform an inspection to determine how and why the failure occurred, and whether or not it should have been noticed and remediated prior to the mishap.