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{{Short description|Test of jet engine durability against broken blades}}
{{Infobox examination
| name = Blade containment and rotor unbalance
| image_name = 166393main Jan07 BladeOutTest.jpg
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| caption = Damaged engine case from blade-out testing. Credit: NASA
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| purpose = Ensures that failure of rotating fan and compressor blades in turbine engines does not cause consequential failures in critical aircraft systems
| year_started = {{Start date|1964}}
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'''Blade off testing''' or '''blade out testing''' is a specific form of [[Air safety#Engine failure|air safety]] testing required by the [[Federal Aviation Administration]] and other safety agencies to certify safety performance of [[jet engine]]s. The tests require engine manufacturers to carry out at least two tests of the engine, to make sure that the engine can survive a [[Jet engine#Compressor blade containment|compressor or fan blade]] breaking off within the engine and a turbine blade breaking off within the engine, without fragments being thrown through the outside enclosure of the engine, creating a [[contained engine failure]].

In the United States, the tests are required by Title 14, Part 33 Subpart F, Section 33.94 of the US [[Code of Federal Regulations]] (CFR), ''Blade containment and rotor unbalance tests''.<ref name=14CFR33.94/><ref name="14CFR">{{cite web |title=Section 33.94 - Blade containment and rotor unbalance tests. (Code of Federal Regulations Title 14 - Aeronautics and Space) |url=https://www.gpo.gov/fdsys/pkg/CFR-2008-title14-vol1/xml/CFR-2008-title14-vol1-sec33-94.xml |website=www.govinfo.gov |publisher=Federal Aviation Administration |accessdate=May 24, 2020 |date=January 1, 2008}}</ref> Equivalent test requirements are provided in the Certification Specifications for Engines (CS-E), published by the [[European Aviation Safety Agency]] (EASA).

==Design==
One of the most challenging component design and certification requirements for commercial jet engines is to mitigate the effects of a "blade-out" rotor failure event, which can result in catastrophic loss of aircraft and/or passengers. Engine blade-out occurs when a sudden change in speed causes a fluctuation in rotor spin and resulting blade overstress condition, or when a blade, or group of blades, fails due to fatigue from repeated cyclic stresses. Testing rotor dynamics and blade-out conditions to ensure safe operation is extremely expensive, time consuming and labor intensive. The testing usually requires a specially prepared compressor or turbine blade with an embedded small explosive charge, to separate it on command during the test.<ref name="NASA 2007">{{cite web | title=Ares I Design and Development Underway at Glenn | work = Aerospace Frontiers| publisher=[[NASA Glenn Research Center]] | date=2007-01-19 | url=https://www.nasa.gov/centers/glenn/news/AF/2007/Jan07_printall.html | access-date=2021-03-02}} {{PD-notice}}</ref>

The tests and standard do not require that the engines continue to operate after the blade failures, only that no fragments penetrate the engine outer casing and that it does not vibrate badly enough during its shutdown that it will tear loose from the aircraft, barring other failures.<ref name=AC33-5/> The [[Society of Automotive Engineers]] have prepared reports detailing the number of blade-out failures.<ref>{{cite report |url=https://www.sae.org/standards/content/air4003/ |title=Report on Aircraft Engine Containment, AIR4003 |date=January 8, 1991 |publisher=SAE International |access-date=10 March 2021}}</ref><ref>{{cite report |url=https://www.sae.org/standards/content/air1537a/ |title=Report on Aircraft Engine Containment, AIR1537A |date=August 1, 1996 |publisher=SAE International |access-date=10 March 2021}}</ref>

There are two approaches to contain debris following a blade-out event: either a hard-wall, which is designed to withstand and deflect shrapnel, or a soft-wall, which is designed to arrest and retain shrapnel. The hard-wall is an older approach dating from the 1970s and tends to be heavier than the soft-wall because it is generally a heavy metal ring; the soft wall generally uses a resilient outer containment layer made from a composite material such as [[aramid fiber]], which requires a larger space to allow the composite layer to expand slightly. In addition, a hard wall to retain solid metal blades generally requires a prohibitively heavy ring, so hard walls are usually used with hollow metal or composite blades.<ref>{{cite news |url=https://aerospaceamerica.aiaa.org/departments/containing-a-blade-out/ |title=Engineering Notebook: Containing a blade-out |author=Button, Keith |date=July–August 2018 |work=Aerospace America |access-date=10 March 2021}}</ref>

A typical hard steel containment ring varied in thickness up to {{convert|3/8|in}} at a weight of {{convert|410|lb}};<ref name=NASA-CR-159544>{{cite report |url=https://ntrs.nasa.gov/citations/19790023177 |title=Containment of Composite Fan Blades, Report No. NASA-CR-159544 |date=July 1979 |author1=Stotler, C.L. |author2=Coppa, A.P. |publisher=National Aeronautics and Space Administration |access-date=10 March 2021}}</ref>{{rp|3;5}} A "stratified containment structure" with a low resistance layer to trap the debris, surrounded by a high resistance layer to maintain the containment shape and minimize further interaction with the remaining turbine blades, was proposed in a 1979 NASA study.<ref name=NASA-CR-159544/>{{rp|9–11}} A compressed air gun was used to fire blade projectiles into several different containment designs to test "stratified" concept designs incorporating composite materials.<ref name=NASA-CR-159544/>{{rp|33;43–77}}

A 1976 study included an evaluation of the armor required to contain the energy from 1 blade, 2 blade, and 4 blade fragments of the compressor and turbine stages of [[General Electric CF6]] and [[Pratt & Whitney JT9D]] engines; although the 4 blade fragment was unlikely to occur, containing it would have required a steel plate {{convert|1.212|in}} thick, adding {{convert|110|to|195|lb}} per engine. The study concluded that redundant armor could be added to the airframe in addition to engine-mounted containment, but at a substantial weight penalty of {{convert|2500|or|3000|lb}} for 3 or 4 engine aircraft, respectively.<ref name=RD77-44>{{cite report |url=http://www.tc.faa.gov/its/worldpac/techrpt/rd77-44.pdf |title=Study to improve airframe engine rotor blade containment, Report No. FAA-RD-77-44 |author=Gunderson, C. O. |date=July 1977 |publisher=U.S. Department of Transportation, Federal Aviation Administration |access-date=10 March 2021}}</ref>{{rp|1–3}} A companion study for engine-mounted armor concluded the weight of a containment to resist a 4 blade fragment would have to increase by approximately {{convert|410|lb}} in addition to the {{convert|510|lb}} of containment material already provided, most of which would be required for the fan section.<ref name=RD77-100>{{cite report |url=https://apps.dtic.mil/dtic/tr/fulltext/u2/a045314.pdf |archive-url=https://web.archive.org/web/20200324083622/https://apps.dtic.mil/dtic/tr/fulltext/u2/a045314.pdf |url-status=live |archive-date=March 24, 2020 |title=Study to improve turbine engine rotor blade containment, Report No. FAA-RD-77-100 |author1=Heermann, Karl F. |author2=McClure, Kenneth R. |author3=Eriksson, Richard H. |date=August 1977 |publisher=U.S. Department of Transportation, Federal Aviation Administration |access-date=10 March 2021}}</ref>{{rp|17–19}}

==History==
===United States===
The original issue of the ''Airworthiness Standards for Aircraft Engines'' ({{CodeFedReg|14|33}}) on June 10, 1964 included a durability requirement in Part 33.19<ref>{{CodeFedReg|14|33|19}}</ref> to ensure "the design of the compressor and turbine rotor cases must provide for the containment of damage from rotor failure."<ref>{{Federal Register|29|7453}}</ref> A series of superseding [[advisory circular]]s (ACs) were issued in 1965,<ref name=AC33-1>{{cite web |url=https://dotlibrary.specialcollection.net/Document?db=DOT-ADVISORY&query=(select+240) |title=AC 33-1: Turbine Engine Foreign Object Ingestion and Rotor Blade Containment Type Certification Procedures |date=June 24, 1965 |publisher=Federal Aviation Agency |access-date=10 March 2021}}</ref> 1968,<ref>{{citation |title=AC 33-1A: Turbine Engine Foreign Object Ingestion and Rotor Blade Containment Type Certification Procedures |date=June 19, 1968 |publisher=Federal Aviation Agency}}</ref> and 1970<ref name=AC33-1B>{{cite web |url=https://www.faa.gov/regulations_policies/advisory_circulars/index.cfm/go/document.information/documentID/22774 |title=AC 33-1B (Cancelled) - Turbine Engine Foreign Object Ingestion and Rotor Blade Containment Type Certification Procedures |date=April 22, 1970 |publisher=Federal Aviation Administration |access-date=10 March 2021}}</ref> to provide guidance to demonstrate compliance to the requirements of the ''Airworthiness Standards''. The 1965 guidance in AC 33-1 noted the favorability of "puncture resistant rotor housings or separate armor adequate to contain broken rotor blades and stator vanes" and engine rotor and bearings strong enough "to provide a strength margin for a period of shutdown and low speed windmilling when large unbalances typical of damaged rotor blading occur," but was more concerned with the mitigation of damage following foreign object ingestion.<ref name=AC33-1/> By 1970, AC 33-1B provided more concrete acceptance criteria for the containment, which should be able to prevent "significant rupture or hazardous distortion of the engine casing and the expulsion of blades through or beyond the edge of the engine case or shield."<ref name=AC33-1B/>

Amendment 10 to the ''Airworthiness Standards'' was published by the [[Federal Aviation Administration]] on February 23, 1984, which modified the durability requirement of 33.19 by adding that "energy levels and trajectories of fragments resulting from rotor blade failure that lie outside the compressor and turbine rotor cases must be defined" and by moving some requirements for blade off testing from the advisory circulars to a new regulation ({{CodeFedReg|14|33|94}}).<ref name=14CFR33.94>{{CodeFedReg|14|33|94}}</ref><ref>{{Federal Register|49|6851}}</ref>

The containment requirement and testing requirement were imposed after review of the history of [[uncontained engine failure]]s which caused serious damage to aircraft, consequent to the July 19, 1989 [[United Airlines Flight 232]] (UA232) accident. That accident did not originate from a fan blade off but from a defect in the fan rotor disk on the Number 2 (tail) [[General Electric CF6]] engine, resulting in a loss of hydraulic power to the flight control actuators and crash landing of that aircraft. One of the recommendations in the resulting [[National Transportation Safety Board]] investigation report was to amend 14 CFR 33 to require an evaluation of engine components; the evaluation would determine which components, if they should fracture and separate, could pose a significant threat to aircraft structures and systems.<ref>{{cite report |url=https://www.ntsb.gov/investigations/AccidentReports/Reports/AAR-90-06.pdf |title=Aircraft Accident Report: United Airlines Flight 232, McDonnell Douglas DC-10-10, Sioux Gateway Airport, Sioux City, Iowa, July 19, 1989 {{!}} NTSB/AAR-90/06 |date=November 1, 1990 |publisher=National Transportation Safety Board |access-date=10 March 2021}}</ref>{{rp|106}} After the UA232 accident, the FAA issued AC 33-5 on June 18, 1990.<ref name=AC33-5>{{cite web |url=https://www.faa.gov/regulations_policies/advisory_circulars/index.cfm/go/document.information/documentID/22780 |title=AC 33-5: Turbine Engine Rotor Blade Containment/Durability |date=June 18, 1990 |publisher=Federal Aviation Administration |access-date=10 March 2021}}</ref>

The UA232 accident also led to new ''Airworthiness Standards'' safety analysis requirements, defining "non-containment of high energy debris" as a hazardous engine effect in Part 33.75,<ref>{{CodeFedReg|14|33|75}}</ref> which was added by Amendment 24 on September 4, 2007;<ref>{{Federal Register|72|50867}}</ref> Amendment 24 also reconciled the United States standards with contemporary European standards.<ref>{{Federal Register|71|5769}}</ref><ref>{{Federal Register|71|40675}}</ref> AC 33-1B was canceled in 2015 after being superseded by newer regulations and ACs.<ref name=AC33-1B/>

===Europe===
The equivalent blade off test requirements were specified in ''Compressor and Turbine Blade Failure'': Subpart E, Section 810 of the [[Joint Aviation Requirements]] for Engines (JAR-E), developed and issued by the [[Joint Aviation Authorities]].<ref>{{cite web |url=http://www.jaa.nl/publications/jars/500980.pdf |title=Amendment 13 to the Joint Aviation Requirements for Engines |date=November 1, 2004 |publisher=Joint Aviation Authorities |archive-url=https://web.archive.org/web/20060526034705/http://www.jaa.nl/publications/jars/500980.pdf |archive-date=May 26, 2006 |url-status=dead}}</ref> JAR-E was superseded by the identically-structured Certification Specifications for Engines (CS-E), initially endorsed and issued by the [[European Aviation Safety Agency]] on October 24, 2003;<ref>{{cite web |url=https://www.easa.europa.eu/document-library/certification-specifications/cs-e-initial-issue |title=CS-E / Initial issue |date=October 24, 2003 |publisher=European Aviation Safety Agency |access-date=10 March 2021}}</ref> the same Subpart E and Section 810 of CS-E apply for blade off testing. Amendment 6 of CS-E 810 states that for a turbine engine to be certified, "it must be demonstrated that any single compressor or turbine blade will be contained after Failure and that no Hazardous Engine Effect can arise as a result of other Engine damage likely to occur before Engine shut down following a blade Failure."<ref>{{cite web |url=https://www.easa.europa.eu/document-library/certification-specifications/cs-e-amendment-6 |title=CS-E Amendment 6 |date=July 1, 2020 |publisher=European Aviation Safety Agency |access-date=10 March 2021}}[https://www.easa.europa.eu/sites/default/files/dfu/Annex%20VII%20%E2%80%94%20CS-E%20Amendment%206%20%281%29.pdf#page=190 direct URL]</ref>

==See also==
* [[Birdstrike simulator]]

==References==
{{nasa}}
{{reflist}}

==External links==
* [http://www.flightglobal.com/articles/2007/05/08/213726/trent-1000-ready-to-fly-following-blade-off-test.html Trent 1000 ready to fly following blade-off test], Flight Global, 2007-05-08
* [https://web.archive.org/web/20080511174756/http://www.investis.com/rollsroyce/presentations/numis.pdf Rolls-Royce - Focused Investment in Technology], 2006
* [https://www.ntsb.gov/investigations/accidentreports/pages/AAR9006.aspx US National Transportation Safety Board, Aircraft Accident Report NTSB/AAR-90-06], November 1, 1990.
* {{youtube |id=wcALjMJbAvU |title=Turbine engine blade fail test}}
* {{youtube |id=j973645y5AA |title=A380 Blade Off Test}}

[[Category:Aircraft engines]]
[[Category:Aviation safety]]

Blade off testing - Revision history

Admin: 1 revision imported

wikipedia>Avinashjohns at 02:45, 27 February 2023