Appendix_A__Proposed_Airworthiness_Bulletin_MILHDBK-516C_(Paragraph_9.1.1)_Revision.pdf

APT RFI Appendix A

Proposed Revision, MIL-HDBK-516C, Paragraph 9.1.1

DRAFT

7 Oct 15

9.1.1 Escape system safety compatibility.

Criterion: Verify that any escape system is compatible with the air system, and that all occupants can safely egress from the aircraft and/or control station.

Standard: An escape system or means of emergency escape is incorporated within the air vehicle for both ground and ditching conditions, and in-flight conditions if specified. (An escape system may include ejection seats, escape capsules, escape path clearance systems, emergency exits, and ground egress aids used to perform the functions of escape, survival, and recovery of air vehicle occupants.) Automated ejection seats, escape capsules or modules function to separate the aircrew from the aircraft and recover them to the earth. Escape system functionality, including operation of escape path clearance systems, does not induce more than a 5% probability of Abbreviated Injury Scale (AIS) 2 or greater injury severity level as defined below throughout the required performance envelope. Means of emergency egress (e.g., use of explosive components for egress, sharp edges, hot metal percussion) does not cause Abbreviated Injury Scale (AIS) 2 or greater injury severity or hinder required procedures for escape, evasion and evacuation. For systems that allow for one or a portion of the aircrew to eject independently, the ability to sustain flight and for remaining aircrew to subsequently eject is not precluded.

Canopies and hatches do not present a risk of collision with any ejectee of the aircraft during the escape and recovery sequence from straight and level flight conditions.

Applied forces during catapult phase do not exceed a 1% probability of AIS 2 injury and free-flight inertial forces during escape do not exceed a 5% probability of AIS 2 injury, as defined below for speeds up to at least 450 Knots Equivalent Air Speed (KEAS). For speeds above 450 KEAS up to the aircraft maximum speed or 600 KEAS, whichever is less (for open ejection seats) the probability of AIS 2 injury does not exceed the levels defined by the injury criteria below.

Note that Control Stations may not have powered or automated egress systems(s).

Specific injury criteria for in-flight escape shown below are met. Unless otherwise noted, the criteria is applicable to the full range of required aircrew anthropometry and aircrew weight range from 103-245 pounds nude weight and full escape envelope up to the aircraft maximum speed or 600 KEAS, whichever is less (for open ejection seats).

a. Accelerations: Catapult phase.

The acceleration imposed on the seat occupant in the +GZ direction (parallel to the spinal column) by the ejection catapult should be limited in terms of Dynamic Response

Index (DRI) values for the z-axis, DRIZ, calculated according to the method described below. The following DRIz limits are for specific catapult pre-ignition temperature and ejected weight representing the ejection seat, personal equipment, and human body weight representative of the crew member population anthropometric range. In addition the following limits are based on a configuration which includes the head rest not more than one inch in front of the seat back tangent line, the seat back tangent line no more than 5o offset from the catapult thrust vector, and standard USAF torso harness with a chest strap and lap belt restraint (or equivalent restraint as determined by 711th HPW).

Ensure the mean seat pan acceleration time history generated at a pre-ignition temperature of 70 °F does not yield a DRIZ value in excess of 16.0 (1% risk of AIS 2 injury) with an allowable standard deviation of 1.0.

Ensure the mean seat pan acceleration time history generated at a pre-ignition temperature of 165 °F does not yield a DRIZ value in excess of 20.0 with an allowable standard deviation of 1.0.

For systems that are inconsistent with the above configuration i.e. head rest more than one inch forward of back tangent line, seat back tangent line more than 5o offset from catapult thrust vector and other harness systems, the DRIz values for all pre-ignition temperatures are reduced by 2 in order to compensate for the differences.

Dynamic Response Index (DRI) Calculation: The DRI is representative of the maximum dynamic compression of the vertebral column of the human body. In physical terms, the human body is described mathematically in terms of an analogous, lumped parameter mechanical model consisting of a mass, spring, and damper. DRI was originally developed for catapult phase only; given the acceleration vector is parallel to the spinal column; within 5o of the z-axis. DRI terms have also been developed for the x-axis (DRIx) and y-axis (DRIy) which can be combined with the original z-axis term (essentially DRIz) to describe acceleration effects on the human body from all axes after the ejection seat has separated from the aircraft (see MDRC below). The compression of the human body along an axis 𝑖𝑖 is captured by the following second order differential equation:

�̈�𝛿𝑖𝑖(𝑡𝑡) + 2𝜁𝜁𝑖𝑖𝜔𝜔𝑛𝑛𝑖𝑖�̇�𝛿𝑖𝑖(𝑡𝑡) + �𝜔𝜔𝑛𝑛𝑖𝑖� 𝛿𝛿𝑖𝑖(𝑡𝑡) = 𝐴𝐴𝑖𝑖(𝑡𝑡)

Where 𝛿𝛿𝑖𝑖(𝑡𝑡) Displacement of the occupant’s body with respect to the critical point

�̇�𝛿𝑖𝑖(𝑡𝑡) Occupant’s relative velocity with respect to the critical point

�̈�𝛿𝑖𝑖(𝑡𝑡) Occupant’s acceleration in an inertial frame 𝜁𝜁𝑖𝑖 Damping coefficient ratio of the dynamic system 𝜔𝜔𝑛𝑛𝑖𝑖 Undamped natural frequency of the dynamic system

𝐴𝐴𝑖𝑖(𝑡𝑡) Measured acceleration along the i-axis of the seat at the critical point

The estimated natural frequency and damping ratio for the Air Force flying population along each axis direction is given in table 1 based on axis orientation as shown in figure 1.

Axis Direction 𝝎𝝎𝒏𝒏 (rad/s) 𝜻𝜻

−𝑋𝑋 Eyeballs Out 60.8 0.04

+𝑋𝑋 Eyeballs In 62.8 0.2

−𝑌𝑌 Eyeballs Left 58.0 0.09

+𝑌𝑌 Eyeballs Right 58.0 0.09

−𝑍𝑍 Eyeballs Up 47.1 0.24

+𝑍𝑍 Eyeballs Down 52.9 0.224

Table 1; Natural Frequency and Damping Ratio Coefficients.

Figure 1; Seat and human axis coordinate system.

The dynamic response for each axis is calculated as follows; where 𝑔𝑔 is the acceleration due to gravity:

𝐷𝐷𝐷𝐷𝑖𝑖(𝑡𝑡) =

�𝜔𝜔𝑛𝑛𝑖𝑖� 𝛿𝛿𝑖𝑖(𝑡𝑡) 𝑔𝑔

At the maximum deflection, the DRI is defined as:

𝐷𝐷𝐷𝐷𝐷𝐷𝑖𝑖 =

�𝜔𝜔𝑛𝑛𝑖𝑖� 𝛿𝛿𝑖𝑖𝑚𝑚𝑚𝑚𝑚𝑚 𝑔𝑔

b. Accelerations: Free-flight and drogue phase (seat/aircraft separation to seat/aircrew separation).

All accelerations shall be limited to meet a Multi-axis Dynamic Response Criterion (MDRC) value not to exceed 1 (5% risk of AIS 2 injury) up to 450 KEAS and may increase linearly, over 450 KEAS, not to exceed 1.5 at 600 KEAS (see figure 2). Where MDRC is defined as:

𝑀𝑀𝐷𝐷𝐷𝐷𝑀𝑀(𝑡𝑡) = ��

𝐷𝐷𝐷𝐷𝑚𝑚(𝑡𝑡)

𝐷𝐷𝐷𝐷𝑚𝑚𝑙𝑙𝑖𝑖𝑚𝑚

𝐷𝐷𝐷𝐷𝑦𝑦(𝑡𝑡)

𝐷𝐷𝐷𝐷𝑦𝑦𝑙𝑙𝑖𝑖𝑚𝑚

𝐷𝐷𝐷𝐷𝑧𝑧(𝑡𝑡)

𝐷𝐷𝐷𝐷𝑧𝑧𝑙𝑙𝑖𝑖𝑚𝑚

𝐷𝐷𝐷𝐷𝑚𝑚,𝑦𝑦,𝑧𝑧 The dynamic response values computed for each x-, y-, and z-axis component of the acceleration time history (see paragraph a for calculation method).

𝐷𝐷𝐷𝐷𝑚𝑚,𝑦𝑦,𝑧𝑧

𝑙𝑙𝑖𝑖𝑚𝑚 The limit value of the dynamic response for each axis direction; as shown in table 2.

Axis Direction Limits (5% Injury Risk)

- X Eyeballs Out

+X Eyeballs In

𝐷𝐷𝐷𝐷𝑚𝑚𝑙𝑙𝑖𝑖𝑚𝑚 = 35

𝐷𝐷𝐷𝐷𝑚𝑚𝑙𝑙𝑖𝑖𝑚𝑚 = 40

- Y Eyeballs Left

+Y Eyeballs right

𝐷𝐷𝐷𝐷𝑦𝑦𝑙𝑙𝑖𝑖𝑚𝑚 = 17

𝐷𝐷𝐷𝐷𝑦𝑦𝑙𝑙𝑖𝑖𝑚𝑚 = 17

- Z Eyeballs Up

+Z Eyeballs Down 𝐷𝐷𝐷𝐷𝑧𝑧lim = 16.5

𝐷𝐷𝐷𝐷𝑧𝑧𝑙𝑙𝑖𝑖𝑚𝑚 = 18

Table 2; MDRC Dynamic Response Limits per axis.

Figure 2; Maximum allowable MDRC value vs. Ejection Speed.

c. Accelerations: Head injury for all phases.

The probability of a concussion (Pconcussion) does not exceed 5% as defined below using the resultant linear and rotational head accelerations where ‘a’ is the observed peak linear acceleration and ‘α’ is the observed peak rotational acceleration as a function of time. Figure 3 shows probability of concussion plotted against ‘a’ and ‘α’.

𝑃𝑃𝑐𝑐𝑜𝑜𝑛𝑛𝑐𝑐𝑛𝑛𝑛𝑛𝑛𝑛𝑖𝑖𝑜𝑜𝑛𝑛 =

1 + 𝑒𝑒−(−10.2+0.0433𝑚𝑚+0.000873𝛼𝛼−0.00000092𝑚𝑚𝛼𝛼)

0.4

0.6

0.8

1.2

1.4

1.6

0 100 200 300 400 500 600 700

M

DR

C (n ot to e xc ee d)

Ejection Speed (KEAS)

MDRC vs. Ejection Speed

Above 450 KEAS; MDRC limit = ((Ejection Speed in KEAS - 450 KEAS)/300 KEAS) + 1

Figure 3; Probability of Concussion vs. Rotational and Linear Acceleration

d. Accelerations: Recovery parachute deployment/inflation phase.

The maximum resultant deceleration/stabilization recovery parachute deployment and inflation loads experienced by the aircrew during escape do not exceed the following maximum resultant chest accelerations and onset rate.

No more than 15 G (vector sum) if the direction of force applied to the body is random and unpredictable as in a typical manual bailout or crew mounted parachute system.

No more than 25 G (vector sum) if the system is controlled so the force is applied while the body is in an optimum position (inertial resultant in +z to −x direction or “eyeballs out” to “eyeballs down.”).

For all cases, G onset rate over the entire rise time portion of the force/time curve should be limited to 100 G/sec.

e. Descent rate: Recovery parachute descent/steady state phase.

Recovery parachute average descent rates do not exceed vertical velocity of 23 ft/sec at sea level (SL) on a standard day.

f. Stability: Free-flight and drogue phase (seat/aircraft separation to seat/aircrew separation).

Seat stability will be maintained to align the neutral axis direction of the aerodynamic deceleration parallel to the eyeballs-out (eyeballs-in for backward facing seats) direction and limit excursions and damped oscillations about the neutral axis to +/- 20O in the pitch or yaw plane.

g. Limb Flail: Windblast, free-flight and drogue phases (seat immersion into airflow to seat/aircrew separation).

Aircraft capable of speeds above 300 knots must incorporate limb restraints (arm & leg) to prevent limb flail. Legacy data indicates probability of flail injuries increases with airspeed and is approximately 5% probability at 300 knots. Leg restraints should prevent movement of the legs laterally beyond the sides of the seat. Arm restraints should prevent movement of arms rearward beyond the seat back tangent line.

h. Neck injury criteria: all phases.

The neck injury criteria detailed below apply through all phases of the ejection with and without helmet mounted displays such as night vision goggles or joint helmet mounted cueing system. This includes cases where deployable head and neck protection devices are used and applies when the devices are deployed in contact with the pilots head/helmet and if the head is out of nominal position when deployed.

Upper neck forces and moments will be limited to meet a Multi-Axial Neck Injury Criteria (MANIC) not to exceed 0.47 and a Neck Moment Index about the x-axis (NMIX) not to exceed 0.56 at the occipital condyles (C0-C1) for speeds up to and including 450 KEAS.

For speeds greater than 450 KEAS the MANIC and NMIx limit may increase linearly as a function of speed up to a MANIC of 0.65 and NMIx of 0.86 at 600 KEAS. MANIC and NMIX are defined below with individual critical values as shown in table 3. The probability of AIS 2 or greater injury corresponding to the MANIC value is shown in figure 4.

MANIC (identified as MANIC(Gy) by Parr) is defined as:

𝑀𝑀𝐴𝐴𝑀𝑀𝐷𝐷𝑀𝑀 = ��

𝐹𝐹𝑋𝑋

𝐹𝐹𝑋𝑋𝑐𝑐𝑋𝑋𝑖𝑖𝑋𝑋

𝐹𝐹𝑌𝑌

𝐹𝐹𝑌𝑌𝑐𝑐𝑋𝑋𝑖𝑖𝑋𝑋

𝐹𝐹𝑍𝑍

𝐹𝐹𝑍𝑍𝑐𝑐𝑋𝑋𝑖𝑖𝑋𝑋

𝑀𝑀𝑌𝑌

𝑀𝑀𝑌𝑌𝑐𝑐𝑋𝑋𝑖𝑖𝑋𝑋

𝑀𝑀𝑍𝑍

𝑀𝑀𝑍𝑍𝑐𝑐𝑋𝑋𝑖𝑖𝑋𝑋

NMIX is defined as:

𝑀𝑀𝑀𝑀𝐷𝐷𝑚𝑚 =

𝑀𝑀𝑚𝑚

𝑀𝑀𝑚𝑚𝑐𝑐𝑋𝑋𝑖𝑖𝑋𝑋

Where:

Fx = observed x direction shear loading Fxcrit = critical intercept value for x direction shear loading Fy = observed y direction shear loading Fycrit = critical intercept value for y direction shear loading Fz = observed axial loading (+Fz = tension, -Fz = compression) Fzcrit = critical intercept value for axial loading (different for tension/compression) Mx = observed moment about the anatomical x axis (side bending) Mxcrit = critical intercept value for side bending

My = observed moment about the anatomical y axis (sagittal plane anterior/posterior bending, +My = flexion, -My = extension) Mycrit = critical intercept value for sagittal plane moments (different for flexion/extension) Mz = observed moment about the anatomical z axis (neck twisting) Mzcrit = critical intercept value for neck twisting

Manikin

Neck Size

Manikin Mass

Human Mass Component Force Component Moment

(lbs) (lbs) (lbs) (N) (in-lbs) (N-m)

Small Female

Hybrid III (for 103-pound manikin)

103 <114

Fxcrit 405 1802

Mxcrit

593 67 Fycrit -Mycrit

(extens) -Fzcrit (comp) 872 3880 Mzcrit +Fzcrit (tens) 964 4287 +Mycrit (flex) 1372 155

125 114- 130.5

Fxcrit

496 2206 Mxcrit

845 95 Fycrit -Mycrit

(extens) -Fzcrit (comp) 1099 4889 Mzcrit +Fzcrit (tens) 1214 5400 +Mycrit (flex) 1939 219

136 130.5-

Fxcrit

522 2322 Mxcrit

912 103 Fycrit -Mycrit

(extens)

Mid Male

Hybrid III (for 136-pound manikin)

-Fzcrit (comp) 1157 5147 Mzcrit +Fzcrit (tens) 1278 5685 +Mycrit (flex) 2094 237

150 143-161

Fxcrit

561 2495 Mxcrit

1016 115 Fycrit -Mycrit

(extens) -Fzcrit (comp) 1243 5529 Mzcrit +Fzcrit (tens) 1373 6107 +Mycrit (flex) 2333 264

172 161-186

Fxcrit

625 2780 Mxcrit

1195 135 Fycrit -Mycrit

(extens) -Fzcrit (comp) 1385 6160 Mzcrit +Fzcrit (tens) 1530 6806 +Mycrit (flex) 2744 310

200 186-210 Fxcrit 683 3038 Mxcrit 1364 154 Fycrit -Mycrit

(extens)

Large Male

Hybrid III (for 200-pound manikin)

-Fzcrit (comp) 1513 6730 Mzcrit +Fzcrit (tens) 1671 7433 +Mycrit (flex) 3133 354

220 210- 232.5

Fxcrit

777 3456 Mxcrit

1584 179 Fycrit -Mycrit

(extens) -Fzcrit (comp) 1673 7440 Mzcrit +Fzcrit (tens) 1847 8216 +Mycrit (flex) 3673 415

245 232.5+

Fxcrit

836 3719 Mxcrit

1850 209 Fycrit -Mycrit

(extens) -Fzcrit (comp) 1853 8243 Mzcrit +Fzcrit (tens) 2047 9106 +Mycrit (flex) 4248 480

Table 3, MANIC and NMIX upper neck critical values based on body mass.

Figure 4; Probability of neck injury vs. MANIC and NMIX values.

As plotted above in figure 4, the probability of AIS 2+ injury based on the MANIC value is defined by:

𝑃𝑃(𝐴𝐴𝐷𝐷𝐴𝐴 ≥ 2) =

1 + 𝑒𝑒6.185−6.85∗𝑀𝑀𝑀𝑀𝑀𝑀𝑀𝑀𝑀𝑀

0 0.5 1 1.5 2 2.5

Pr ob ab ili ty o f A

IS

N ec k In ju ry

MANIC NMIx

As plotted above in figure 4, the probability of AIS 2+ injury based on the Neck Moment Index about the x-axis (NMIX) value is defined by:

P(AIS≥2)=

1+ e5.2545-4.1*NMIx

i. Escape Capability.

Ejection seat systems will have the capability for escape at zero altitude (in level flight) from zero airspeed to maximum velocity of the aircraft or 600 KEAS whichever is less (for an open ejection seat). In low altitude, adverse attitude conditions automated escape systems will be capable of escape at the conditions shown in table 4. This applies to the full range of occupant CG locations for the specified aircrew population anthropometry within +/- 2 inches from the main rocket thrust line.

Altitude

(Feet)

Velocity

(Knots)

Attitude

Fore and Aft Roll Angle

01 120 Level 60O

200 150 Level 180O

3002 150 Level 0O

500 200 60O Nose down 0O

500 450 30O Nose down 0O

550 200 60O Nose down 60O

600 250 45O Nose down 180O

In all cases the cited conditions are at the initiation of the catapult

1. Aircraft impact with the ground occurs at instant of seat-aircraft separation.

2. 10,000 foot per minute sink rate.

Table 4; Low Level Escape Performance

Method of Compliance: Inspection of engineering drawings verifies the escape system has all components necessary to allow aircrew escape. System level performance as integrated into the aircraft is verified by testing throughout the designated envelope with extreme permutations of crew anthropometry and mass properties. System level testing (such as sled tests and canopy jettison/fracture tests) using US Air Force approved instrumented articulating dummies verifies that exposure to acceleration levels and other loads, forces, environments, and impacts do not exceed injury criteria and injury probability levels. Emergency egress demonstrations with human subjects verify the ability to safely operate required systems and egress the air vehicle. System level testing, analysis, and subsystem level test and demonstration verify integration and compatibility with the air vehicle and other subsystems (e.g., structural testing/analysis, electromagnetic compatibility testing, power/electrical system tests, software verification testing, aerodynamic analysis).

References: JSSG-2010-3: 3.3.4

JSSG-2010-7: 3.7.3.5.3

JSSG-2010-11: 3.11.7, 3.11.7.2

JSSG 2010-12: 3.12.2.2

Parr, Jeffrey, “A Method to Develop Neck Injury Criteria to Aid Design and Test of Escape Systems Incorporating Helmet Mounted Displays”, AFIT/DS/ENV/14-01.

Rowson, Steven and Duma, Stefan, “Brain Injury Prediction: Assessing the Combined Probability of Concussion Using Linear and Rotational Head Acceleration”, Annals of Biomedical Engineering, Vol. 41, No.5, May 2013.

Gennarelli, Thomas & Wodzin, Elaine, editors, “Abbreviated Injury Scale 2005, Updated 2008”, Association for the Advancement of Automotive Medicine, Oct 2008.