F-111 Crew Module Escape and Survival Systems

A tutorial by Kevin Coyne.

F-111.net thanks Kevin for permission to host this page.
Kevin is the webmaster of the 'Ejection Site' http://www.bestweb.net/~kcoyne/

This document comes from a self-study text and is primarily an introduction. Text and graphics have been edited to improve readability, but content is unchanged.

Static test firing of the prototype F-111 ejection module.(source Scott White)

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The development of the high-speed F-111 aircraft caused the need for an improved egress system. The ejectable crew module was designed to meet this need. The system provides maximum protection for the crewmembers throughout the aircraft performance envelope and includes capabilities for safe ejections at maximum speed and altitude as well as at zero altitude and 50 knots indicated airspeed (KIAS). The module is self-righting, watertight, has flotation provisions, and provides protection for the crewmembers from environmental hazards met on land or water. A side-by-side crew arrangement facilitates safe and effective performance and allows crewmembers to work together and aid one another in performing mission tasks while still maintaining their forward visibility which is an important factor in high-speed, low-level flights.

In this unit we will look at the many systems that make up the crew module. We will break these systems down into components, tie these components together and trace the ejection sequence.

Chapter 1. Escape and Survival Systems Description

The crew module is composed of many systems such as:

• Initiation.
• Severance.
• Separation.
• Stabilization.
• Recovery.
• Landing.
• Flotation.
• Survival.
• Seat and restraint.
• Emergency oxygen.

They are interconnected by means of shielded mild detonating cord (SMDC) which acts as a stimulus transfer medium. The SMDC is provided with time delay initiators (TDI) and one-way explosive transfers to ensure proper sequencing of the various functions. Explosive transfer connectors are incorporated in the system for firing redundancy. After actuation of the initiation system, sequencing of all systems through landing and flotation is automatic. The escape and survival systems consist of the crew module system and oxygen systems. The oxygen systems are the normal (liquid) oxygen system, oxygen quantity and pressure warning system, and emergency (gaseous) oxygen system.

219. System overview

Now that you have a general idea of what makes up the crew module ejection system, let's take a closer look at the module system and the oxygen system. Let's begin with the crew module.

Crew module. The crew module, (fig. 1 ), provides maximum comfort and protection for both crewmembers during normal and emergency conditions. It is integrated into the F-111 aircraft encompassing the pressurized cabin and forward portion of the wing glove. The two crew seats are positioned side by side and have restraints incorporated that enhance freedom of movement and comfort by eliminating the need for a personal parachute and survival equipment to be fitted to the crewmembers. Survival equipment and a recovery parachute are a part of the crew module system. During an emergency, the crew module is separated from the aircraft and propelled to a height sufficient for successful recovery throughout the aircraft performance envelope. The system has features to reduce the landing shock on land or water and has self-righting buoyancy, flotation capacity, and protects the crewmembers against environmental hazards.

Oxygen system. The three functions of the oxygen systems are normal, quantity and pressure warning, and emergency. During normal operations, the normal (liquid) oxygen system supplies the crewmembers with breathing oxygen. When the normal oxygen system malfunctions, low system pressure and low liquid oxygen quantities are indicated by a normal oxygen quantity and pressure warning system.

Figure 1. F-111 crew module.

An emergency (gaseous) oxygen system supplies breathing oxygen to crewmembers during normal oxygen system failure or during an ejection.

220. Pre-ejection

As stated earlier, the crew module escape system is made up of many systems which work together during an ejection. These systems can be divided into three categories: pre-ejection, ejection, and post-ejection. The pre-ejection category consists of the ejection initiators, guillotines, emergency oxygen, mechanical explosive interrupt, a radio beacon, a 3.0-second TDI, chaff, and a .35-second TDI. Let's take a closer look at some of the components that may be unfamiliar to you.

Ejection initiators. The ejection initiators are used to start the sequence to separate and eject the crew module from a disabled aircraft, much like the ejection initiators used in any other aircraft. However, as you can see in figure 2, the initiators used in the F-111 are quite different in looks and operation. Safety pins are normally installed in the ejection initiator handles to prevent accidental firing of the initiators, whenever aircraft maintenance is being performed.

An ejection initiator on each side of the center console is within easy reach of both crewmembers and permits either crewmember to start the crew module ejection sequence. Each initiator has a D-shaped grip that must be squeezed and then pulled upward to actuate the built-in firing mechanism. Squeezing the grip releases the initiator's built-in lock release. As the grip is pulled, the firing mechanism first compresses the firing pin springs. As the grip reaches its upper limits, the spring tension drives the firing pins into a percussion-type primer. The primer actuates the explosive train and the explosive crossover.

Figure 2. Ejection initiator.

Guillotines. Guillotines sever antenna leads, secondary control cables, and an oxygen line. Refer to the guillotines in figure 3. The cartridge is fired by the SMDC to actuate the guillotine blade for severance. The secondary controls guillotine is located on the bottom surface of the crew module floor in the left cheek area of the fuselage, the blade antenna leads guillotine is located on the centerline of the crew module glove beneath access cover 2410, and the leading edge antenna leads guillotine is located on the centerline of the crew module glove beneath access cover 2420.

Figure 3. Guillotine assemblies.

Emergency oxygen. The emergency oxygen system provides both crewmembers with a 10-minute supply of oxygen during ejection or when the normal aircraft oxygen system fails. During the pre-ejection sequence, the emergency oxygen system is actuated explosively by the SMDC from the ejection initiators. If the normal oxygen system fails during flight, the emergency system can be turned on manually.

Mechanical explosive interrupt (MEI). The MEI is a unit, that is controlled by the crewmember with a chaff interrupt lever, that allows or stops the explosive propagation to the emergency radio beacon and the 3.0-second TDI which, when fired, actuates the chaff dispenser. If the unit is closed, then propagation is stopped. The TDI and emergency radio beacon are not activated. If the unit is open, then propagation continues, activating both the emergency radio beacon and a 3-second TDI. The TDI gives the crew module time to clear the aircraft before it fires, actuating the chaff dispenser.

Radio beacon. The radio beacon sends out radio signals for rescue purposes after an ejection. If the MEI is in the open position, the beacon will automatically send out its signal. If the MEI is closed, the radio beacon can be manually operated by a switch in the cockpit.

.35-second TDI. The .35-second time-delay initiator is fired by the SMDC from the ejection initiators and delays the actuation of the components that make up the severance system.

221. Ejection

Now let's look at the ejection category which consists of flexible linear-shaped charges (FLSC), two. 15-second time-delay initiators, a rocket motor, a dual mode, q-actuated selector, a 1.6-second time-delay initiator, a 4.4-second time delay initiator, a 1.0-second time-delay initiator, a "G" sensor initiator, and the select/interrupt valve.

Flexible linear-shaped charge. FLSC severs the module from the aircraft. It is installed around certain covers and splice plates on the module to cut the metal for severance and is formed in a chevron-shaped cross section for use in severance strips. Also, it is used to cut a larger hole in the upper nozzle of the rocket motor during high-speed ejections. A booster tip is installed on each end. The amount of explosive per foot of FLSC is selected to cut a specified thickness of metal.

.15-second TDI. Them are two .15-second time-delay initiators installed in the ejection system. One delays firing of the stabilization/brake parachute catapult until the module has separated from the aircraft and the other delays firing of the FLSC in the rocket motor upper nozzle in mode 1 until the module has cleared the aircraft.

Rocket motor. In figure 4, you see that the rocket motor is composed of an upper closure or compartment, a 9-inch by 58-inch steel cylinder case, and a lower closure or compartment. Starting at the top of the upper closure, the SMDC propagation actuates the firing pin. This in turn fires the percussion primer in the igniter cup, which then detonates the motor ignition pellets. These ignition pellets are suspended in a foam that aids in their detonation. The rapidly detonating ignition pellets cause the propellant grain in the steel cylinder to be ignited.

Figure 4. Rocket motor.

The rocket motor lower nozzle provides 27,000 pounds of thrust. To avoid excessive "g" forces to the crewmembers, the rocket motor is provided with two concentric upper nozzles, secondary and auxiliary. The small auxiliary nozzle in the center of the upper nozzle fires simultaneously with the lower nozzle. This action provides 500 pounds of thrust to counteract slow-speed crew module pitch up at speeds below 300 knots. At speeds above 300 knots, after a .15-second delay, the upper nozzle burst diaphragm is severed by a flexible linear-shaped charge (FLSC) to increase the exhaust-flow area, thus increasing its thrust. Because of the increase in the exhaust-flow area, the rocket motor operating pressure is lowered, which results in reduced thrust of 9,000 pounds at the lower nozzle and increases the upper nozzle thrust to 7,000 pounds. This overall decreased thrust extends the operating time and reduces excessive "g" forces.

Dual-mode, q-actuated selector. In figure 5, you see the dual-mode, q-actuated selector. It continuously senses aircraft speed and selects the appropriate time delay. The letter "q" is used to identify forces or pressure required to actuate various pressure-sensitive aircraft devices. Pressure from the pitot static system, or ram pressure, is sensed at one end of the q-actuated selector, while dynamic pressure is sensed at the other end. Due to differential pressure, the q-actuated selector allows activation of a 1-second TDI to the barostat lock initiator and blocks propagation to the rocket motor upper nozzle when aircraft speed is less than 300 knots. When aircraft speed is greater than 300 knots, differential pressure is changed so that the q-actuated selector blocks propagation to the 1-second TDt and allows activation of SMDC to the. 15-second TDI to the rocket motor upper nozzle to fire.

Figure 5. Dual-mode, q-actuated selector.

4.4-second TDI. Another explosive train, with a 4.4-second time-delay initiator, is provided to back up both the dual-mode, qactuated selector and the g-sensor initiator. This equipment ensures that the barostat lock initiator is never activated more than 4.4 seconds after the rocket motor is fired.

1.0-second TDI. This time delay allows the module to gain altitude during a mode 1 ejection. Upon actuation, it fires the barostat lock initiator.

G-sensor initiator. The g-sensor initiator (fig. 6) is located in the survival equipment explosive device compartment. A TDI delays firing the g-sensor initiator for 1.6 seconds after rocket motor ignition during high-speed ejections. The forward motion of the crew module may be relatively high immediately after ejection of the crew module at speeds above 300 knots. After the forward motion decreases to approximately 2.2 (+/- 1 ) g' s, the g-sensor initiator fires and activates the barostat lock initiator.

Figure 6. Dual-mode, q-actuated selector.

Select/interrupt valve. The select/interrupt valve works similarly to the mechanical explosive interrupt. It either allows or blocks explosive propagation leading to the stabilization/brake parachute cutters. The direction of propagation depends on the mode of ejection selected by the dual-mode, q-actuated selector. When a mode 1 is selected, a detonation transfer assembly (DTA), which is another type of mild detonating cord, repositions the select/interrupt valve. When the recovery system operates, DTA propagation passes through the repositioned valve and fires the cutters.

222. Post ejection (recovery system)

The post ejection system consists of the barostat lock initiator, the recovery parachute catapult, the recovery parachute, a 3.0-second TDI, a 7.0-second TDI, the impact attenuation bag, the UHF antenna, the recovery parachute repositioning release retractor, and the stabilization/brake parachute cutters. Let's begin our discussion of this category with the barostat lock initiator.

Barostat lock initiator. The barostat lock initiator (fig. 7) consists of two operating trains. Normally, an aneroid bellows in each explosive train is locked to prevent firing of the train, constant cycling, and wear-out. Firing of the SMDC into the barostat inlet port initiates an explosive charge that retracts the pins which normally lock the bellows. The aneroid bellows prevents the firing of the explosive train until the module falls to within 14,000 and 16,000 feet. Below this pressure altitude, atmospheric pressure compresses the bellows sufficiently to release the firing pins that initiate the booster caps and continue the detonation sequence to remove the recovery parachute and blade antenna severable cover and fire the recovery parachute catapult. The barostat lock initiator is located on the explosive component support bracket in the rocket motor compartment.

Figure 7. Barostat lock initiator.

Recovery parachute. In figure 8, you see the recovery parachute, a 70 foot, flat-diameter, ring sail parachute equipped with a reefing line cutter. Reefing lines prevent the large parachute from fully opening until the suspension lines are fully stretched. The parachute is stowed in a compartment aft of the left crew seat bulkhead.

The recovery parachute is deployed into the airstream by a recovery parachute catapult. The parachute is assisted in extending by a small pilot parachute. The recovery parachute is deployed in a reefed or partially inflated condition to reduce the opening shock of the parachute to the crew module. When the suspension lines are fully stretched, the reefing line is cut by the reefing line cutter to allow the parachute to fully blossom. The recovery parachute is then suspended as it appears in the smaller illustration on the right in figure 8.

Figure 8. Recovery parachute.


Module of FB-111A 68-243 showing less than optimum landing situation.  The pilot of this aircraft suffered minor injuries from tree branch penetration of the module floor during the assent. (Image via www.FB-111.net )

3.0-second TDI. The 3.0-second time-delay initiator allows for recovery parachute deployment before activating the nitrogen bottles for the impact attenuation bag.

7.0-second TDI. This time delay allows the recovery parachute to fully blossom before firing the FLSC to free the UHF antenna. It also fires the recovery parachute repositioning release retractor.

Impact attenuation bag. The impact attenuation bag (fig. 9) is made of neoprene coated nylon cloth and is stored under the crew compartment. The bag has several interconnected chambers; and when these chambers are inflated, the bag serves as a cushion and absorbs the landing shock of the crew module.

Figure 9. Impact Attenuation Bag.

The bag contains blowout plugs of various sizes. These plugs are retained by shear pins. Upon landing, the pins shear to release the blowout plugs, allowing the bag to deflate which reduces shock of crew module impact to within allowable limits.

UHF antenna. FLSC severs the UHF antenna cover after 7 seconds. Once the cover has been severed, the UHF antenna is free to extend and send out radio signals from the radio beacon.

Recovery parachute repositioning release retractor. There are three release retractors provided in the recovery system. These retractors are the recovery parachute repositioning release retractor, aft release retractor, and forward release retractor. Each retractor operates the same mechanically. The repositioning release retractor provides a means for greater recovery loads to be absorbed by the parachute clevis and to release this clevis for crew module repositioning and parachute bridle deployment. After landing, the forward and aft release retractors provide a means for releasing the recovery parachute bridle lines and thus the recovery parachute from the crew module. Upon firing the retractor cartridge by means of SMDC, gas pressure actuates the retractor pin assembly into the refractor housing to release the attached components.

Stabilization/brake parachute cutters. These cutters are fired by a detonation transfer assembly and release the stabilization/brake parachute during mode 1 ejection.

223. Stabilization system

The stabilization system consists of the stabilization/brake parachute catapult, the stabilization/brake parachute, stabilization glove, stabilization flaps, and pitch flaps. Let' s begin our discussion of this system with the stabilization/brake parachute.

Stabilization/brake parachute. This is a 6-foot diameter hemisphere-type parachute that, by means of bridle lines, is attached to the crew module at the aft end of the stabilization glove. The parachute is pressure packed around the outer barrel of the parachute catapult and stored in a compartment on the top aft end of the stabilization glove.

After the stabilization/brake parachute severable cover is severed, the parachute catapult is fired. This ejects the parachute and catapult outer barrel aft and upward from the stabilization glove. As the bridle lines pull tight, the outer barrel strips the deployment bag from the parachute. This permits the parachute to deploy, slowing the module down and providing lateral stability. If the ejection takes place below 300 knots, the stabilization/brake parachute is cut away from the module concurrent with recovery parachute deployment to prevent possible entanglement of the two parachutes.

Stabilization glove. The stabilization glove is an integral part of the crew module and is also the forward part of the aircraft wing. This glove section serves to stabilizes the flight of the crew module by preventing pitch down after its separation from the aircraft and until the recovery parachute is supporting the module. It also houses the aft flotation bags and the stabilization/brake parachute.

Stabilization flaps. The stabilization flaps are located forward of the forward pressure bulkhead on the lower surface bulkhead. They are stowed in the retracted position and, when released, extend approximately 64ø from the forward pressure bulkhead. At high speeds, the flap linkage stretches under aerodynamic forces so that the flaps rotate to approximately 79ø. The spring-actuated stabilization flaps, (which are released upon separation of the crew module from the aircraft), reduce crew module pitch up at transonic speeds following separation from the aircraft.

Pitch flaps. The pitch flaps are attached to a hinged metal frame with a compressed spring, on the lower aft end of the stabilization glove. Upon separation of the crew module from the aircraft, the compressed spring actuates the pitch flaps to the lowered position. A synchronizing cable, routed through pulleys on both flaps, assures simultaneous deployment. The pitch flaps lower the trim angle of the module approximately 10ø to assist in horizontal stability.

Self-Test Questions

219. System overview

1. How are the crew seats arranged and how have they been designed for freedom of movement and comfort?

2. What are the three functions of the oxygen system?

3. What is the purpose of the quantity and pressure warning function of the oxygen system?

220. Pre-ejection

1. What is required to be done to the ejection initiators whenever aircraft maintenance is being performed?

2. Where are the guillotines located?

3. How is the emergency oxygen system actuated?

4. What is the MEI used for in the ejection sequence?

5. What is the radio beacon used for and how is it operated?

221. Ejection

1. How is FLSC used throughout the F-111 module system?

2. What is the purpose of the .15-second TDI's installed in the ejection system?

3. How is the rocket motor designed to avoid excessive "g" forces?

4. What is the purpose of the 4.4-second TDI in the pre-ejection?

5. What is the purpose of the select/interrupt valve?

222. Post-ejection

1. What components make up the post ejection system?

2. Where is the barostat lock initiator located?

3. How is the recovery parachute initially deployed?

4. What is the purpose of the repositioning release retractors?

223. Stabilization system

1. How and where is the stabilization/brake parachute stored?

2. During ejections below 300 knots, when is the stabilization/brake parachute cut away from the module and why?

3. What is the purpose of the stabilization glove?

4. Upon separation of the crew module from the aircraft, how are the pitch flaps actuated?

Chapter 2. Crew Module Ejection Sequence

As stated earlier, the crew module ejection systems are interconnected by means of shielded mild detonating cord (SMDC). To ensure proper sequencing of functions, SMDC uses time-delay initiators and one-way explosive transfers. Explosive transfer connectors also are incorporated in the systems for firing redundancy. After ejection begins, the sequence of events is rapid, in fact almost simultaneous. Delay initiators in the systems, however, do delay firing of certain components until other parts of the explosive system are fired. Refer to figure 10 as you study this system.

224. Ejection Sequence.

Figure 10. Crew Module Ejection Sequence.

Figure 11. SMDC.

Crew Module operation. Ejection is initiated by actuating either of the ejection initiators. The ejection initiators detonate the SMDC which provides a simultaneous transfer medium for the the crew module. Each end of the SMDC lines has has a stainless steel booster tip (fig 11). Propagation from one booster tip to another is accomplished by the impact of the shrapnel formed by fragmentation of the thin stainless steel booster tip sheathing. The detonation rate of the SMDC is 20,000 to 25,000 feet per second with an associated pressure front of 3 to 4 million psi.

As SMDC propagation occurs, the following events occur.

1. Both powered inertia-lock retraction devices fire to retract the upper restraint harness restraining the crewmembers.
2. The secondary controls guillotine is actuated to sever secondary control cables and the normal oxygen hose, the blade antenna leads guillotine is actuated to sever the coaxial antenna leads, and the leading edge antenna leads guillotine is actuated to sever the leading edge antenna leads in the wing.
3. The emergency oxygen system is activated.
4. The propagation of SMDC continues to the mechanical explosive interrupt which allows or stops the propagation as the crewmember desires. If the unit is closed then propagation is stopped. The chaff dispenser and emergency radio beacon are not activated. If the unit is open, then propagation continues and activates the emergency radio beacon and a 3.0 second time-delay initiator. The time-delay initiator gives the crew module time to clear the aircraft before it fires, actuating the chaff dispenser.
5. The 0.35-second time-delay initiator is activated. This time-delay initiator delays firing of the rocket motor and severance of the crew module until steps a through e have occurred. Severance. After an interval of 0.35 second, the time-delay initiator fires, causing the following events:
   1. The 0.15-second time-delay initiator is activated delaying firing of the stabilization/brake parachute catapult until after the crew module has left the aircraft.
   2. The rocket motor is ignited.
   3. The backup SMDC to the guillotines, emergency oxygen system, and chaff dispenser is detonated. This portion of the system is provided in the event of failure of the SMDC when ejection is initiated.
   4. The FLSC is detonated, severing the crew module mating devices from the aircraft and the stabilization/brake parachute severable cover from the crew module. At the same moment the FLSC severs the crew module from the aircraft, the 1.6 and 4.4-second time-delay initiators are activated. At this point, the dual-mode, q-actuated selector determines which route the SMDC takes. The q-actuated selector senses aircraft speed and determines whether the aircraft speed is above or below 300 knots so that it can select the appropriate time delay.

Separation. When the module is completely severed from the aircraft, the rocket propels the crew module up and away from the aircraft. After a 0.15-second delay, the stabilization/brake parachute catapult is fired and deploys the parachute.

At speeds below 300 knots, the dual-mode, q-actuated selector prevents propagation to the rocket motor upper nozzle diaphragm FLSC assembly, and activates a 1.0-second delay initiator and DTA lines going to the select interrupt valve. At this point, the select interrupt valve is repositioned allowing the stabilization/brake parachute cutters to release the stabilization/brake parachute during the low-mode ejection. The 1-second delay allows the crew module to clear the aircraft and stabilize in flight, before the recovery parachute is deployed. After a 1-second delay, the initiator will fire and activate the barostat lock initiator. The barostat lock initiator, when fired, activates the recovery system and releases the stabilization/brake parachute.

At ejection speeds above 300 knots, the dual-mode, q-actuated selector prevents propagation to the 1.0-second delay initiator and DTA lines leading to the select/interrupt valve and allows propagation to activate the 0.15-second time delay initiator. Since the selector interrupt is not repositioned during high-speed ejections, the stabilization/brake parachute remains attached to the module throughout the ejection sequence. Firing of the 0.15-second time-delay initiator continues SMDC propagation to the rocket motor upper nozzle FLSC assembly to sever the diaphragm. Because the barostat lock initiator cannot be activated through the dual-mode, q-actuated selector above ejection speeds of 300 knots, a 1.6-second time-delay initiator is provided. This initiator delays SMDC propagation to the g-sensor initiator for 1.6 seconds after rocket motor ignition. Once the 1.6-second time delay has elapsed, the initiator activates the g-sensor initiator. After the forward speed of the crew module slows down to approximately 2.2 g's, the g-sensor initiator fires, activating the barostat lock initiator.

Another explosive train, with a 4.4-second time-delay initiator, is provided to back up both the dual-mode, q-actuated selector and the g-sensor initiator.

225. Time-Delay Initiation

At this point, the module has separated from the aircraft and is on its descent. Now let's discuss the events that take place during this phase of ejection. Descent. Upon activation of the barostat lock initiator, the aneroid bellows are released. The firing pins are retained by the bellows until the crew module falls to between 16,000 and 14,000 feet. When the firing pins are released, detonation occurs. Propagation continues to the recovery parachute cover FLSC, DTA leading to the select interrupt valve, and the recovery parachute catapult. The parachute cover FLSC and recovery parachute catapult are fired simultaneously, causing the catapult to deploy the recovery parachute. The DTA line coming off the cover going to the select interrupt valve is activated also. However, depending on whether the select interrupt valve was previously repositioned by the q-actuated selector determines whether the stabilization/brake parachute is released from the module. At this point, the crew module is fastened to the recovery parachute by the repositioning release retractor. At the same time the recovery parachute catapult is fired, the 3- and 7-second time-delay initiators are activated. The 3-second time delay allows the recovery parachute to blossom before actuating the impact attenuation bag system. After the 3-second TDI is fired, propagation is continued to sever the attenuation bag cover with the FLSC and fire the pressure source explosive valve. This releases compressed gas to inflate the attenuation bag. If automatic recovery parachute deployment fails, the recovery parachute deploy initiator is provided.

After a delay of 7 seconds, the parachute repositioning release retractor is activated to release the recovery parachute clevis. As the parachute pulls away from the module, it deploys the forward and aft bridle lines. The bridle lines that connect the recovery parachute to the crew module forward and aft release retractors, permit the crew module to assume a level landing position. At the same time the repositioning release retractor fires, the emergency UHF antenna actuator is fired to extend the antenna.

You see in figure 12 that just before landing, the severance and flotation initiator handle is actuated to provide inflation of the self-righting and aft flotation bags (detail A shows the aft flotation bags, and detail B shows the self-righting bags). Detonation shock waves from the severance and flotation initiator are propagated through the SMDC to fire the aft flotation and left self-righting bag pressure source, a 75-second time-delay initiator, and FLSC which severs the self-righting and aft flotation bag covers from the crew module. The pressure source explosive valve is simultaneously activated to release compressed gas to both aft flotation bags and the left self-righting bag. The 75-second time delay is provided to allow the crew module to settle on land, or if a water landing is made, to allow it to surface.

Figure 12. Self-Righting and Aft Flotation Bags.

Landing. After firing of the 75-second time delay initiator, the right side self-righting bag pressure source valve is activated This action releases compressed gas to inflate the bag. If the crew module is inverted, it is pushed to an upright position as the bag inflates

Upon landing on the ground or water, the landing shock is absorbed by controlled deflation (blowout plugs expelled) of the impact attenuation bag Immediately upon landing, the recovery parachute release initiator handle is actuated

Propagation through the SMDC actuates the release retractors and releases the recovery parachute from the crew module. This prevents dragging of the crew module along the ground by high winds, or if a water landing was made, from being pulled under the surface.

If, after a water landing, additional buoyancy is required to keep the crew module afloat, the auxiliary flotation bag is deployed. This is accomplished by pulling the auxiliary flotation handle. Propagation through the SMDC simultaneously fires the FLSC to cut the severable cover and actuates the pressure source explosive valve. This releases compressed gas to inflate the bag.

If the aircraft is ditched in water and the crew module is still attached to it, it can be released by actuating the severance and flotation initiator handle. Propagation through the SMDC will sever the module from the aircraft and activate the emergency oxygen system, aft flotation system, and self-righting system. At this time, the crew module is resting in an upright position, and it provides the crewmembers with shelter until they are rescued.

Self-Test Questions

224. Ejection sequence

1. How is SMDC propagation transferred from one line to another?

2. List the events that occur when the ejection control initiators are fired.

3. Upon detonation of the FLSC, during the severance phase, what components are severed?

4. What is the purpose of the 1.0-second time delay initiated by the dual-mode, q-actuated selector?

5. What is the purpose of the 4.4-second time-delay initiator?

Newspaper Clipping about the ejection of F-111F 70-2418 (via Jonathan Sayers)

Flag Gifs from 3dflags.com