Approach to fuselage structural fuel tank protection against pool fires

Wednesday, March 16, 2022: 4:30 PM
103 (Pasadena Convention Center)
Dr. R.C. Alderliesten , Delft University of Technology, Delft, Netherlands
Prof. Jan Willem Gunnink , GTM Advanced Structures, The Hague, Netherlands
J.H. Halm , Royal NLR – Netherlands Aerospace Centre, Amsterdam, Netherlands
P. Kortbeek , Fibre Metal Laminate Centre of Competence, Delft, Netherlands
After receiving an application for a major type design change for a civil transport aircraft, EASA decided for a special condition subject to a public consultation. The features requiring the special condition relate to the proposal for an integral (structural) rear centre tank, which “brings additional risks (explosion, penetration by fire, ..) if it is exposed to an external fire”[1]. Aside from the fire penetration identified here as potential risk, another concern raised identifies “the possibility of tank internal volume heating from the external pool-fed fire threat resulting in explosion or ignition of flammable vapors”[2].

To address such concern and to comply to the special condition, an advanced hybrid structure is proposed based on the Fibre Metal laminate (FML) concept, successfully applied by Airbus in the Airbus A380 skin. The concept adopts the FML baseline, with known and demonstrated excellent burn-through resistance (enabling over 5 minutes evacuation time), complemented with additional layers for enhanced insulating purposes, if demanded. Rather than relying on insulating (non-structural) materials, this hybrid concept incorporates the insulating features into the advanced FML panel design.

To demonstrate the burn-through and insulating capabilities of these FML configurations, various panel configurations have been exposed to Bunsen burner tests, where burn-through time and backside temperatures were recorded. The results are correlated to a GLARE4B-5/4-0.4 baseline panel with nominal 3.6 mm thickness, and a monolithic aluminium panel of 6 mm thickness. With the results it is explained how FMLs, such as GLARE, previously certified for primary fuselage structural skin applications, can easily be modified to comply to recent special conditions issued by EASA.

[1] EASA, Passenger Protection from External Fire, SC-D25.856-01, 18 January 2021: https://www.easa.europa.eu/sites/default/files/dfu/sc-d25.856-01_issue-01_-_final_post_consultation_0.pdf

[2] Mildred Troegeler,Director, Global Regulatory Strategy, The Boeing Company, Comment Nr.2, Comment Response Document dated 24 February 2021: https://www.easa.europa.eu/sites/default/files/dfu/crd_-_sc-d25.856-01_issue-01_0.pdf

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