AMC 22.561 Emergency Landing Conditions – General

CAA ORS9 Decision No. 1

For maximum protection of the occupants in survivable crash landings, the main part of the cockpit, defined in AMC 22.561(b)(2), should constitute a safety cell strong enough to comply with paragraph CS 22.561(b)(2).

The forward part should be sufficiently weaker for it to yield before the main part, but stiff enough for it to absorb considerable energy in doing so. (ref. 2, 4, 5, 8, 9, 11)

Energy-absorbing seats, seat cushions or seat mountings constitute another means of improving safety by reducing the load on the occupants head and spine in a crash (ref. 1, 3, 10) and /or landing with retracted wheels (CS 22.561(c)).

The wording „give every reasonable chance” expresses the limited possibility to determine the quantitative probability of injuries in the process, which is affected by many random inputs (e.g.: physical weight and height of the occupant, his age, influencing the spinal load resistance, specific characteristics of the particular accident etc.).

The required load level has been chosen partly on medical grounds and partly in consideration of what is currently practicable. The objective is to design a cockpit structure that does not collapse under survivable emergency landing conditions.

Furthermore the sailplane design should consider:

    — Maximum energy absorption, and

    — Occupant protection against serious injuries, namely injuries of head and spine.

    For maximum protection of the foremost part of legs during the front part deformation, the feet should have adequate space to move slightly backwards together, without twisting or rocking.

    The conditions specified in this paragraph are considered to be most representative of the wide envelope of possible crash loads and impact directions (ref. 5, 9). However the design should be such that the strength is not unduly sensitive to load direction in pitch or yaw.

    Further information about different aspects of the crashworthiness of small aircraft design has been accumulated for small airplanes (ref. 6). Published data and procedures are also applicable for sailplane designs.

    Applicable information on dynamic computer modelling contained in (ref. 7) might be used to assess applicability of such methods for sailplanes crashworthiness tasks.

    Note: Compliance with the revised CS 22.561 requirements would also assure the adequate structural characteristics for safe ground impact when Sailplane Parachute Rescue System is applied. (ref. 4,12)

    References:

    (1) Chandler. R.F.

    Injury Criteria Relative to Civil Aircraft Seat and Restraint Human Systems. SAE TP Series No. 851847. (Publication 1985)

    (2) Hansman, R.J., Crawley, E.F., Kampf, K.P.

    Experimental Investigation of the Crashworthiness of Scaled Composite Sailplane Fuselages. Technical Soaring Vol. 14 No 4. ISSN #0744-8996 (1990)

    (3) Segal, A.M., McKenzie, L., Neil, L., Rees, M. Dynamic Testing of Highly Damped Foam.

    Technical Soaring Vol. 19 No 4. ISSN #0744-8996 (1995)

    (4) Rőger, W., Conradi, M., Ohnimus, T

    Insassensicherheit bei Luftfahrtgerät. Fachhochschule Aachen. Forschungsbericht im Auftrag des Bundesministerium für Verkehr 1996 (Publication December 1996)

    (5) Sperber, M.

    Crashworthiness in Glider Cockpits.

    OSTIV XXV Congress paper 1997, St Auban

    Untersuchung des Insassenschutzes bei Unfällen mit Segelflugzeugen und Motorsegler Forschungsauftrag Nr.L- 2/93-50112/92, TÜV Rheinland, Köln/Rh. Germany, 1998

    (6) Hurley, T.R., Vandenburg, J.M.

    Small Airplane Crashworthiness Design Guide, AGATE-WP3.4-034043-036 Simula Technologies, Phoenix AZ, USA. (Publication April 2002)

    (7) FAA ACE 100

    FAA Methodology for Dynamic Seats Certification by Analysis. AC 20 -146, FAA, USA (Publication date 5/19/03)

    (8) Boermans, L., Nicolossi, F., Kubrynski, K.,

    Aerodynamic Design of High Performance Sailplane Wing Fuselage Combination. ICAS-98-2, 9, 2 Publication. (Publication 1998)

    (9) Sperber, M. et al.

    Energy absorption on landing accidents with sailplanes and powered sailplanes Rep. No. FE-

    Nr.L-2/2005-50.0304/2004, TÜV Rheinland, Köln /Rh., Germany, 2007

    (10) Segal, A.M.,

    Energy Absorbing Seat Cushions for use in Gliders. Technical Soaring Vol. 32, No 1/2. ISSN #0744-8996 (2008)

    (11) Röger, W.

    Safe and Crashworthy Cockpit

    Fachhochschule Aachen, Fachbereich Luft-und Raumfahrttechnik,Germany, 2007

    (12) Röger, W.

    Verbesserung der Insassensicherheit bei Segelflugzeugen und Motorsegler durch integrierte Rettungssysteme, Forschungsauftrag Nr. L-2/90-50091/90, Fachhochschule Aachen, Germany, 1994.