Abstract:
An air cargo device for facilitating the movement and retention of unit load devices on an air cargo deck includes a base member on which are mounted a caster roller, a guide and a restraint. The guide and the restraint are coaxially mounted and together occupy one of three positions: both the guide and restraint being recessed; the guide raised with the restraint recessed, and both the guide and restraint being raised. One end of the base member is provided with retractable tension studs suitable for mating with a portion of a seat track, while the opposite end of the base member is provided with shoulder bolts for mating with a lock tray. This permits the device to bridge between the two types of cargo floor fixtures.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
   None. 
   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention is related to a guide and restraint assembly suitable for retaining centerline-mounted air cargo loading unit load devices, such as pallets. 
   2. Background 
   Commercial aircraft carry cargo in containers and pallets, referred to collectively as unit load devices (ULDs). ULDs are available in several different standard configurations with different lengths and widths. During loading and unloading operations, ULDs must be guided within the cargo compartment. During flight, ULDs must be retained to prevent damage to the aircraft and the cargo. Floor-mounted devices, such as guides and restraints are typically used for these purposes and some such devices (referred to herein as a “guide/restraint”) serve both functions. 
   The deck of a Boeing 747 main cargo compartment is configured with a multitude of longitudinally extending retaining devices such as seat tracks (sometimes referred to as “seat rails”) and lock trays to which such guides, restraints and guide/restraints (collectively, “conveying devices”) are attached. A number of these retaining devices and conveying devices are positioned to accommodate some containers in predetermined locations in a side-by-side configuration along the centerline of the 747 main cargo deck. 
   From time to time, a 747 main cargo compartment must carry out-sized cargo (i.e., cargo that does not fit in standard positions because it would interfere with the inside contour of a cargo hold). An example of out-sized cargo might be a large turbine engine which, due to its large width and circular profile, cannot be loaded in a standard location close to the cargo hold sidewall. In such case, the out-sized cargo is loaded onto a standard-size pallet which in then placed along the centerline of the cargo hold. Currently, standard-sized pallets for air cargo transport are approximately 96 inches wide and either 20 feet, 16 feet or 10 feet in length. Mounting such a pallet along the centerline results in the long sides of a pallet extending about 48 inches on either side of the centerline. 
   Currently, the 747 cargo deck is not equipped with guide/restraints that are suitable for both guiding containers and retaining centerline mounted pallets. As a result, on a 747 main cargo deck, a centerline loaded pallet is normally tied down using straps. This method of restraining the pallet requires a large amount of manpower, requiring a number of personnel trained to properly strap cargo securely. It also delays the unloading of the such cargo, due to the time it takes to safely remove the straps at the destination. 
   SUMMARY OF THE INVENTION 
   In one aspect, the present invention is directed to an air cargo transportation device capable of both guiding and restraining ULDs. The device includes a base having a first end and a second end, a first guide mounted to the base and rotatable between a retracted position and an upright position, and a lockhead mounted to the base and rotatable between a retracted position and an upright position, wherein the first guide and the lockhead are coaxially arranged. 
   The first end of the base is provided with tension studs suitable for engaging a seat track and also with shear bosses suitable for engaging a seat track. The shear bosses may be located outside a load span defined by the tension studs. 
   The second end of the base may be provided with bolts for engaging a lock tray. 
   A caster may be mounted to the base between the first and second ends. 
   The first guide and the lockhead may be coaxially mounted on a common shaft that is proximate the second end of the base. 
   The device may be arranged such that, when the lockhead is in the retracted position, the lockhead can be rotated from the retracted position to the upright position only (a) if the first guide is also rotated from the retracted position to the upright position at the same time, or (b) if the first guide is already in the upright position. 
   A rotatably mounted pawl having a pair of spaced apart legs may be used to maintain the lockhead in the upright position, the spaced apart legs abutting the lockhead. 
   A pair of spaced apart guide pawls fixedly mounted on a shaft may be used to engage a lower portion of the first guide and maintain it in the upright position. The shaft may also include a release handle mounted thereon which, when activated, releases the lower portion of the first guide and allows the first guide to return to the retracted position. 
   Furthermore, when both the first guide and the lockhead are in the upright position, the lockhead is taller than the first guide and projects in a first direction towards the first end of the base, past the forwardmost point of the first guide extending in said first direction. 
   The air cargo transportation device may further comprise a second guide mounted to the base and rotatable between a retracted position and an upright position, the first guide and second guide both being mounted proximate the second end of the base. 
   In another aspect, the present invention is directed to an air cargo deck configured to restrain a pallet along its centerline. The air cargo deck has first and second rows of air cargo transportation devices mounted therein, the first and second rows extending parallel to, and on opposite sides of, the centerline, each row comprising a plurality of air cargo transportation devices. Each such air cargo transportation device comprises a base having a first end and a second end, a first guide mounted to the base and rotatable between a retracted position and an upright position, and a lockhead mounted to the base and rotatable between a retracted position and an upright position, wherein the first guide and the lockhead are coaxially arranged. The air cargo transportation devices are mounted in the cargo deck such that the first end of each base is closer to the centerline than the second end of that base, the first end of each air cargo transportation device is attached to a seat track, and the second end of each air cargo transportation device is attached to a lock tray. The first guide and the lockhead may be proximate to the second end. 
   In yet another aspect, the present invention is directed to a method of loading a pallet on an air cargo deck having a centerline. The method entails providing the air cargo deck arranged as described above, positioning the pallet such that it straddles the centerline with long sides of the pallet overlying a portion of the base of at least some of said air cargo transportation devices in each row, and then rotating the lockheads of said at least some of said air cargo transportation devices in each row from the retracted position to the upright position, to thereby retain the pallet in position. Prior to positioning the pallet, one or more items of out-sized cargo may be placed on the pallet. 
   In still another aspect, the present invention is directed to a method of converting an air cargo deck so that it can accommodate centerline loading of a pallet without the use of straps. In this instance, the air cargo deck already has first and second seat tracks extending parallel to the centerline and positioned on either side thereof, and also first and second lock trays extending parallel to the centerline and positioned on either side thereof. Each of the first and second lock trays is spaced apart from a corresponding seat track and is farther from the centerline that its corresponding seat track. The inventive method comprises installing a first plurality of air cargo transportation devices between the first seat track and the first lock tray, and installing a second plurality of air cargo transportation devices between the second seat track and the second lock tray. Each such installed air cargo transportation device comprises a base having a first end and a second end, a first guide mounted to the base and rotatable between a retracted position and an upright position, and a lockhead mounted to the base and rotatable between a retracted position and an upright position, wherein the first guide and the lockhead are coaxially arranged. The first guide and the lockhead may be proximate to the second end of the base. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  shows a front perspective view of a first embodiment of a guide/restraint in accordance with the present invention, with the guide and lockhead both in the upright position. 
       FIG. 2  shows a rear perspective view the guide/restraint of  FIG. 1  with the base seen in phantom. 
       FIG. 3A  show a U-shaped pawl configured to support the rotated lockhead in the upright position 
       FIG. 3B  shows a rotatable lockhead which serves as the restraint member. 
       FIG. 3C  shows a rotatable guide member which serves as the main guide. 
       FIG. 4  shows the base of the guide/restraint of  FIG. 1 . 
       FIG. 5A  shows a first exploded view illustrating the assembly of the guide/restraint of  FIG. 1 . 
       FIG. 5B  shows a second exploded view illustrating clusters of components belonging to shaft and pin assemblies around which the guide, the lockhead, the lockhead pawl and the guide pawls rotate. 
       FIG. 6  shows a view of  FIG. 1  with the base seen in phantom. 
       FIG. 7 . shows a front perspective view of the embodiment of  FIG. 1 , with the guide and lockhead both in the retracted position. 
       FIG. 8 . shows a view of  FIG. 7  with the base seen in phantom. 
       FIG. 9 . shows a rear perspective view the guide/restraint of  FIG. 7  with the base seen in phantom. 
       FIG. 10  shows a front perspective view of the embodiment of  FIG. 1 , with the guide in the upright position, the lockhead in the retracted position and the base in phantom. 
       FIG. 11  shows a rear perspective view of  FIG. 10   
       FIG. 12  shows a rear perspective view of the guide/restraint of  FIG. 1  with the base seen in phantom, highlighting the operation of the lockhead pawl and lockhead. 
       FIG. 13  shows a side view of the embodiment of  FIG. 8 . 
       FIG. 14  shows a side view of the embodiment of  FIG. 10 . 
       FIGS. 15A and 15B  show two perspective views of a guide/restraint secured at one end to a lock tray and at opposite end to a seat track. 
       FIG. 16  shows a front perspective view of a second embodiment of a guide/restraint in accordance with the present invention, having an auxiliary guide in the upright position. 
       FIG. 17  shows a front perspective view of the guide/restraint of  FIG. 16 , with the base shown in phantom and the auxiliary guide in the retracted position. 
       FIG. 18  shows an exploded view of the guide/restraint of  FIG. 16 . 
       FIG. 19  shows a rear perspective view of the guide/restraint of  FIG. 16 , with the base shown in phantom and the auxiliary guide in the upright position. 
       FIG. 20  shows a partial layout of an air cargo deck in which a pallet is loaded along the centerline and retained with guides/restraints in accordance with the present invention. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
     FIG. 1  shows a perspective view of a guide/restraint  100  in accordance with a first embodiment of the present invention with both the rotatable guide  122  and the rotatable lockhead  124  in the upright position. As seen in the rear perspective view of  FIG. 2 , a rotatable U-shaped lockhead pawl  126  supports the lockhead  124 . 
   As seen in  FIG. 3A , the U-shaped lockhead pawl  126  has a pair of pawl legs  128 A,  128 B which are spaced apart at their inner surfaces by a distance D. The legs  128 A,  128 B are connected by a cross member  129  having an aperture  127  for receiving ends of lockhead pawl torsions springs  190 A,  190 B ( FIG. 2 ). Each pawl leg  128 A,  128 B is provided with a corresponding opening  131 A,  131 B for rotatably mounting the lockhead pawl  126  on a lockhead pawl shaft  133  ( FIG. 5A ). The pawl legs  128 A,  128 B have lower ramping surfaces  123 A,  123 B, respectively, whose significance is described below with respect to operation of the lockhead  124  and  FIGS. 11 and 12 . Furthermore, the ends  130 A,  130 B of the pawl legs  128 A,  128 B, respectively, serve as abutment surfaces which abut against rearwardly facing surfaces  132  formed in a notch  134  of the lockhead  124  ( FIG. 3B ). It is these ends  130 A,  130 B which support the lockhead  124  when the latter is in the upright position of  FIGS. 1 and 2 . A flange  128 C on the side of one leg  128 B provides a handle of sorts to facilitate hand or foot operation of the lockhead pawl  126 . 
   As seen in  FIG. 3B , the lockhead  124  includes a pair of spaced apart lockhead legs  136 A,  136 B in which a pair of openings  137 A,  137 B, respectively, are formed. The openings  137 A,  137 B permit the lockhead  124  to be rotatably mounted on a lockhead shaft  139  ( FIG. 5A ). The lockhead&#39;s spaced apart legs  136 A,  136 B are connected by an upper lockhead body  138  terminating in a forwardly projecting lock  140 . It is the underside surface  140 A of the lock  140  which, when deployed during flight, is juxtaposed against a lip or other formation on an ULD, thereby retaining such ULD in place. The transverse width W of the lock  140  is narrower than spacing D between the legs  128 A,  128 B of the lockhead pawl  122 . Upper portions of the lockhead&#39;s legs  136 A,  136 B are provided with shoulders  135 A,  135 B (only one being shown in  FIG. 3B ). As seen in  FIG. 3B , the shoulders  135 A,  135 B each are provided with a beveled surface  141  proximate the front side of the lockhead body  138 . The lower portion of the body  138 , on a front side thereof, is provided with a pair of channels  143 A,  143 B configured to accommodate ends of outer torsion springs  180 A,  180 B, which bias the lockhead  124  towards the retracted (down) position. 
   As seen in  FIG. 3C , the rotatable guide  122  has a pair of spaced apart guide legs  150 A,  150 B connected by a guide cross member  152  having a backside  152 A and a front side  152 B ( FIG. 1 ). The lower portion of the guide cross member  152  is provided with a pair of apertures  159 A,  159 B into which ends of inner torsion springs  182 A,  182 B are inserted to bias the guide  122  towards the retracted (down) position. Thus, both the guide  122  and the lockhead  124  are normally biased toward the retracted position in which they recline in the recesses  170 ,  172 , described below. 
   The guide legs  150 A,  150 B are provided with openings  151 A,  151 B, respectively, which permit the guide  122  to be rotatably mounted on the lockhead shaft  139  ( FIG. 5A ). Thus, the guide  122  and the lockhead  124  are coaxially arranged and, in the embodiment shown, are mounted on and share the common lockhead shaft  139 . The lockhead legs  136 A,  136 B are spaced apart by a first distance that is smaller than a second distance between the guide legs  150 A,  150 B. Accordingly, in the guide/restraint  100 , the lockhead legs  136 A,  136 B are nested between the guide legs  150 A,  150 B along the lockhead shaft  139 . Thus, the guide  122  and the lockhead  124  are separate members having dissimilar shapes and sharing a common axis of rotation around which each is rotatable relative to the base  102 . 
   At their lowermost portion, the guide legs  150 A,  150 B are provided with forwardly facing cutouts  153 A,  153 B, respectively. As discussed further below, when the rotatable guide  122  is the upright position, the cutouts  153 A,  153 B are engaged by spaced apart, upwardly biased guide pawls  160 A,  160 B ( FIGS. 6 ,  10  &amp;  14 ), respectively, which are mounted on a guide pawl shaft  161  and secured thereto by guide pawl shaft pins  163 . The lower portions of the guide legs  150 A,  150 B, on their back sides, are provided with curved abutment surfaces  149 A,  149 B, respectively. As discussed further below with respect to  FIG. 8 , these abutment surfaces  149 A,  149 B abut and move along riding surfaces of the upwardly biased guide pawls  160 A,  160 B, when the guide  122  is adjusted from the retracted position to the upright position. 
   Attached to an upper portion of guide leg  150 B is an outwardly extending, wedge-shaped guide head  154 . The guide head  154  has a rearwardly facing hollow back side  155  and a rearwardly beveled front side  157 . The forwardly facing front side  152 B of the cross member  152 , and the rearwardly beveled front side  157  of the guide head  156  together form a continuous guide abutment surface  158  for guiding ULDs, when the guide head  156  is in the upright position ( FIG. 1 ). 
   As seen in  FIGS. 1 and 4 , the guide/restraint  100  includes a base  102  having a top surface  104 . Formed in the top surface  104  of the base  102  is a circular recess  106  for accommodating a roller-type caster  108 . The caster  108  is positioned between the guide  122  and a first, or ‘inboard’ end  110  of the base  102 . The caster  108  is itself mounted on a swiveling base, allowing it to pivot and self-align with an ULD passing overhead. The caster  108  provides vertical support for a bottom of a passing ULD to help eliminate sagging ULD edges. 
   The first or ‘inboard’ end  110  of the base  102 , at lower portion thereof, is provided with integrally formed shear bosses  112  and spring biased tension studs  114  having an elongated lower portion  115  ( FIG. 5A ). The shear bosses  112  and the tension studs  114  are configured to engage a seat track  410 , as discussed further below. Tension stud nuts  116  and washers  118  ( FIGS. 5A &amp; 5B ) maintain the tension studs  114  in place. The tension studs  114  are spaced apart by a distance K, and define the transverse extent of the guide/restraint&#39;s load span. 
   As seen in  FIG. 2 , the second or ‘outboard’ end  120  of the base  102  is provided with openings  119  into which removable shoulder bolts  121  may be inserted, for securely attaching the guide/restraint  100  to a lock tray, as discussed further below. Thus, in this embodiment, opposite ends  110 ,  120  of the base  102  are provided with different types of fixation devices  114 ,  121  for attaching to dissimilar retaining devices mounted on an air cargo deck. 
   As seen in the embodiment of  FIG. 4 , the axially extending long sides  210 A,  210 B of the base are not parallel to one another, although this is not a requirement of the present invention. In the embodiment shown, one side  210 A is provided with a gusset  220  which widens a portion of the base proximate the inboard end  110  where the shear bosses  112  are located. Providing such a gusset  220  helps distribute a vertical load applied to the guide/restraint  100  via shear bosses  112 . The shear bosses  112  are outside the load span K ( FIG. 1 ) defined by the spacing between tension studs  114 , and so a vertical load may be directed to positions outside the normal load span K. 
   Again with reference to  FIG. 4 , the top surface  104  of the base  102  also includes a pair of recesses  170 ,  172  proximate the outboard end  120 . Of these, recess  172  has a forward recess portion  172 A and a rearward recess portion  172 B. 
   As seen in  FIG. 7 , recess  170  is configured to receive the wedge-shaped guide head  156 , when the guide  122  is in the retracted position. 
   With reference to  FIGS. 4 ,  5 A,  5 B and  6 , the forward recess portion  172 A accommodates the lockhead legs  136 A,  136 B (best seen in  FIG. 3B ), the lockhead shaft  139 , and a lockhead sleeve  184  mounted on the lockhead shaft  139 . The forward recess portion  172 A also accommodates two pairs of torsion springs which are mounted on the lockhead sleeve  184 . The two pairs of torsion springs include a first inner pair  182 A,  182 B configured to bias the guide  122  towards the retracted position, and a second outer pair  180 A,  180 B configured to bias the lockhead  124 , also towards the retracted position. 
   In the embodiment shown, the guide legs  150 A,  150 B ( FIG. 3C ) are accommodated in narrow slots  186 A,  186 B located on either side of the forward recess portion  172 A and separated therefrom by intermediate recess walls  188 A,  188 B, respectively. Slot  186 B communicates with guide head recess  170 . As seen in  FIG. 4 , the forward recess portion  172 A, on a first sidewall thereof, has a forward journalled opening  174 A for supporting the lockhead shaft  139 . The opposing second sidewall (hidden in  FIG. 4 ) of the forward recess portion  172 A has a similar forward journalled opening (also hidden in  FIG. 4 ). 
   A first pair of bushings  183 A,  183 B are positioned in the lockhead leg openings  137 A,  137 B, respectively, to facilitate rotation of the lockhead  124 . Meanwhile, a second pair of bushings  185 A,  185 B are positioned in the guide openings  151 A,  151 B, respectively, to facilitate rotation of the guide  122 . A lockhead shaft securing pin  139 A is used to ensure that the lockhead shaft  139  stays in place. 
   The lockhead shaft  139 , the lockhead shaft securing pin  139 A, the lockhead sleeve  184 , the inner and outer pairs of torsion springs  182 A,  182 B and  180 A,  180 B, respectively, and the first and second pairs of bushings  183 A,  183 B and  185 A,  185 B, respectively, together form a lockhead shaft assembly  230  ( FIG. 5B ). 
   Again with reference to  FIGS. 4 ,  5 A and  6 , the rearward recess portion  172 B accommodates the pawl legs  128 A,  128 B, the lockhead pawl shaft  133 , and a lockhead pawl sleeve  192  mounted on the lockhead pawl shaft  133 . The rearward recess portion  172 B also accommodates a pair of lockhead torsion springs  190 A,  190 B which are mounted on the lockhead pawl sleeve  192 , and downwardly biases the lockhead pawl  126 . As seen in  FIG. 4 , the rearward recess portion  172 B, on a first sidewall thereof, has a rearward journalled opening  174 B for supporting the lockhead pawl shaft  133 . The opposing second sidewall (hidden in  FIG. 4 ) of the forward recess portion  172 A has a similar forward journalled opening (also hidden in  FIG. 4 ). 
   A pair of bushings  193 A,  193 B ( FIG. 5B ) are positioned in the lockhead pawl openings  131 A,  131 B ( FIG. 3A ), respectively, to facilitate rotation of the lockhead pawl  126  around the lockhead pawl shaft  133 . A lockhead pawl shaft securing pin  133 A is used to ensure that the lockhead pawl shaft  133  stays in place. 
   The lockhead pawl shaft  133 , the lockhead pawl shaft securing pin  133 A, the lockhead pawl sleeve  192 , the lockhead torsion springs  190 A,  190 B, and the bushings  193 A,  193 B together form a lockhead pawl shaft assembly  232  ( FIG. 5B ). 
   As best seen in  FIG. 4 , the top surface  104  of the base  102  is also provided with a pair of openings  194 A,  194 B for receiving the guide pawls  160 A,  160 B which, as stated above, are mounted on the guide pawl shaft  161 . The sidewalls within each of the openings  194 A,  194 B are provided with pairs of opposing apertures  196  for supporting horizontally aligned tension spring pins  198 A,  198 B. The tension spring pins  198 A,  198 B, in turn, each support one end of a tension spring  200 A,  200 B, respectively. The second ends of the tension springs  200 A,  200 B are anchored in an aperture ( FIG. 6 ) formed within the guide pawls  160 A,  160 B, respectively. 
   The axis of the guide pawl shaft  161  is offset relative to the axes of the directions in which the guide pawls  160 A,  160 B are upwardly biased. Therefore, the tension springs  200 A,  200 B urge the guide pawl shaft  161  to rotate in the direction indicated by the rotational arrow R, as shown in  FIG. 6 . 
   As seen in  FIGS. 2 and 6 , a first end  202  of the guide pawl shaft  161  is provided with a manually operable release handle  204 . The release handle  204  is secured to the guide pawl shaft  161  via a release handle pin  206 . The guide pawl shaft  161 , the release handle  204 , the guide pawls  160 A,  160 B, the tension springs  200 A,  200 B, and the various pins associated with each of these, together form a guide pawl shaft assembly  234  ( FIG. 5B ). 
   As best seen in  FIG. 4 , a long side  210 A of the base  102  is provided with a number of apertures  212 ,  214  and  216 . Aperture  212 , which has a mate  222  on the opposite long side  2101 B of the base  102  ( FIG. 2 ), permits the insertion of the lockhead pawl shaft  133  and other members of the lockhead pawl shaft assembly  232 . Aperture  214 , which also has a mate  224  on the opposite long side  210 B of the base  102  ( FIG. 2 ), permits the insertion of the lockhead shaft  139  and other members of the lockhead shaft assembly  230  ( FIG. 5B ). Lastly, aperture  216 , which also has a mate (not seen) on the opposite long side  210 B of the base  102 , permits the insertion of the guide pawl shaft  161 . 
   Operation of the guide/restraint  100  is explained next.  FIG. 7  shows the guide/restraint  100  with both the guide  122  and the lockhead  124  in the retracted position.  FIG. 8  shows a view similar to  FIG. 7 , but with the base shown in phantom. With the guide/restraint  100  deployed on a cargo deck and the guide  122  and the lockhead  124  both in the retracted position, an ULD may travel along a transport plane of the cargo deck, above the retracted guide  122  and lockhead  124 . As best seen in  FIG. 9 , the guide  122  overlies the lockhead  124  when both are in the retracted position. Thus, the guide  122  must first be rotated to the upright position ( FIG. 10  and  FIG. 11 ) before the lockhead  124  can be rotated. In other words, the lockhead  124  can be rotated from the retracted position to the upright position only if the guide  122  is also rotated from the retracted position to the upright position at the same time, or, if the guide  122  is already in the upright position ( FIG. 10  and  FIG. 11 ). 
   As seen in  FIGS. 8 and 13 , when the guide  122  is in the retracted position, curved abutment surfaces  149 A,  149 B ( FIG. 3C ) formed on the back side of the guide legs  150 A,  150 B, respectively, abut and rest upon forward portions of the upwardly biased guide pawls  160 A,  160 B. As the guide  122  is manually rotated from the retracted position of  FIGS. 8 and 13  to the upright position of  FIGS. 10 and 14 , the lower portion of the guide legs  150 A,  150 B rotate and the curved abutment surfaces  149 A,  149 B ride on forward portions of the guide pawls  160 A,  160 B until the ends of the upwardly biased guide pawls  160 A,  160 B are received into the forwardly facing cutouts  153 A,  153 B formed on the guide legs  150 A,  150 B. Thus, the guide  122  is locked in the upright position by a pair of spaced apart, upwardly biased, guide pawls  160 A,  160 B, fixedly mounted on the common guide pawl shaft  161 . 
   With reference to  FIGS. 10 and 11 , to return the guide  122  to the retracted position, an operator rotates the release handle  204  of the guide pawl shaft assembly  234  in the direction indicated by the rotational arrow S. This causes the ends of the guide pawls  160 A,  160 B to disengage from the forwardly facing cutouts  153 A,  153 B formed on the guide legs  150 A,  150 B, thereby releasing the guide  122 . And since the guide  122  is biased towards the retracted position by the inner springs  182 A,  182 B, the released guide  122  snaps back to assume the retracted position of  FIGS. 8 and 13 . 
   With reference to  FIGS. 3A ,  3 B,  11  and  12 , the process for adjusting the lockhead  124  from the retracted position to the upright position is now explained. An operator grabs the lock  140  of the lockhead  124  and begins to rotate the lockhead  124  towards the upright position. As this happens, the shoulders  135 A,  135 B, and especially their beveled surfaces  141  ( FIG. 3B ) first abut the lower ramping surfaces  123 A,  123 B on the lockhead pawl&#39;s legs  128 A,  128 B, respectively. As the operator continues to rotate the lockhead  124 , its shoulders  135 A,  135 B travel along the length of the lower ramping surfaces  123 A,  123 B, rotating the lockhead pawl  126  about its shaft  133  against the biasing force of springs  190 A,  190 B, and lifting its legs  128 A,  128 B. As the lockhead  124  is rotated into the fully upright position, the lockhead pawl&#39;s legs  128 A,  128 B slip off the shoulders  135 A,  135 B, and the end surfaces  130 A,  130 B fall into place against rearwardly facing surfaces  132  formed in a notch  134  of the lockhead  124 . In this manner, the lockhead pawl  126  locks the lockhead  124  in the upright position, as seen in  FIG. 12 . 
   As seen in the figures, when both the guide  122  and the lockhead  124  are in the upright position, the lockhead  124  is taller than the guide  122  and the lockhead&#39;s lock  140  projects past the forwardmost point of the cross-member  152  of the guide  122  in the forward (or ‘inboard’) direction. This allows the lock  140  and/or its underside surface  140 A to abut or otherwise engage a pocket or other structure formed on a pallet. So, even though the guide  122  is in the upright position, it does not interfere with using the lockhead  124  due to the construction of these two components and also because of their coaxial arrangement. 
   When both the lockhead  124  and the guide  122  are in the upright position, one must first return lockhead  124  to the retracted position; operating the release handle  204  with the lockhead  124  will not return the guide  122  to the retracted position. To return the lockhead  124  to the retracted position, an operator further rotates the lockhead pawl  126  by foot or by hand, perhaps at the flange  128 C, so that the end surfaces  130 A,  130 B of the lockhead pawl  126  are lifted upwards past the notch  134 . Since the outer springs  180 A,  180 B bias the lockhead  124  towards the retracted position, and the lockhead  124  is no longer supported by the end surfaces  130 A,  130 B due to the operator&#39;s action, the lockhead  124  snaps back into the retracted position, its lock  140  passing between the legs  128 A,  128 B of the lockhead pawl  126 . After the lockhead  124  has been released, the operator then releases the lockhead pawl  126 , allowing it to return to the retracted position by virtue of the biasing force of springs  190 A,  190 B. This results in the guide/restraint  100  being returned to the position seen in  FIG. 7 . 
   From the foregoing, it can be seen that when the lockhead  124  is down, the guide  122  is independently operable. Thus, with the lockhead  124  in a retracted position, the guide  122  may be brought to the upright position during loading of a cargo deck to provide guidance for various ULDs. Once a pallet has been loaded, the lockhead  124  may also be brought to an upright position to maintain the pallet in position during flight. 
   To unload a pallet, the lockheads  124  are first retracted so as to disengage from a pocket, or other structure, provided on the pallet. The guides  122 , at least on a first side of the pallet, are then retracted to facilitate removal of the pallet from the cargo deck. In one embodiment, the guides  122  on the opposite side of the pallet may be left in the upright position to facilitate guidance of other ULDs which had been loaded on the cargo deck. 
     FIGS. 15A and 15B  show a guide/restraint  100  secured at the first, or ‘inboard’ end  110  to a seat track  410  and at the second, or ‘outboard’ end  120  to a lock tray  400 . 
   As seen in these figures, this particular lock tray  400  is mounted to an air cargo floor fixture  404 . The lock tray  400  comprises a pair of parallel rails  402 A,  402 B. In one embodiment, each rail  402 A,  402 B is provided with a linear array of holes  408  spaced apart at one inch centers. Rollers  402  supported by these rails  402 A,  402 B are spaced apart along the length of the lock tray  400 . 
   The outboard end  120  of the guide/restraint  100  is secured to the lock tray  400  by means of the shoulder bolts  121 , which are screwed into openings  119  ( FIG. 2 ) formed in the outboard end wall of the guide/restraint  110 . 
   At its inboard end  110 , the guide/restraint  100  is secured to the seat track  410  by means of the shear bosses  112  and tension studs  114  ( FIG. 1 ) having tension stud nuts  116 . As is known to those skilled in the art, the upper surface of each seat track  410  has a pair of opposing scalloped flanges  411  (only one of the pair being visible in  FIG. 15B ) forming a row of circular openings  412  connected by narrowed lips  413  (only one lip being visible in  FIG. 15B ). The tension studs  114  have an elongated lower portion  115  whose width is narrow enough to fit between the narrowed lips  413  of the opposing scalloped flanges  411 . In one embodiment, installation is performed by first inserting the shear bosses  112  into the circular openings  412  while simultaneously inserting the lower portion  115  of the tension studs  114 , with its long dimension parallel to the length of the seat track  410 , between the narrowed lips  413  of the opposing scalloped flanges  411 . Then, each tension stud  114  is rotated by a quarter turn, i.e., by 90°, so that the long dimension of its lower portion  115  is transverse to the length of the seat track  410 . This results in the tension studs  114  being retained by the undersides of the opposing scalloped flanges  411  of the seat track  410 . 
   It can thus be seen from  FIGS. 1 ,  2 ,  15 A and  15 B, that while one end  110  of the guide/restraint  100  is provided with a first type of fixation device (e.g., tensions studs), the opposite second end  120  is provided with an altogether different type of fixation device (e.g., shoulder bolts). This arrangement allows a guide/restraint  100  to be positioned between dissimilar retaining devices, such as lock trays  400  and seat tracks  410 , having completely different hardware for mating to a device such as the disclosed guide/restraint  100 . 
     FIG. 16  shows a front perspective view of another guide/restraint  600 , in accordance with one embodiment of the present invention. 
   The guide/restraint  600  has a base  602  supporting many of the same, or similar, components seen in the guide/restraint  100  described above. The common components include a caster  508 , a guide  522  having a wedge-shaped guide head  554  provided with a rearwardly beveled front side  557 , a lockhead  524 , a lockhead pawl  526  and a release handle  604  for releasing the guide  522 , all of whose operation is similar to that of their counterparts in  FIGS. 1-14 , described above. 
   In addition, for mating with other floor-mounted retaining devices, the base  602  is provided with shear bosses  512  and tension studs  514  on a first ‘inboard’ end  510 , and is provided with shoulder bolts  521  on a second ‘outboard’ end  520 . Much like the guide/restraint  100  described above, the shear bosses  512  and tension studs  514  are configured to connect to a seat track, such as seat track  410 , while the shoulder bolts  521  are configured to connect to a lock tray, such as lock tray  400 . 
   As seen in  FIG. 16  and  FIG. 18 , the guide/restraint  600  has an auxiliary recess  702 . A wedge-shaped second, or ‘auxiliary’, guide  704  is mounted in this recess  702 . The auxiliary guide  702  comprises an angled front surface  706 , a generally triangular top surface  708 , a back surface  710  ( FIG. 17  and  FIG. 19 ) and a pair of legs  712 A,  712 B having axially aligned openings  714 A,  714 B, respectively. With reference to  FIG. 17  and  FIG. 18 , the auxiliary guide  702  is mounted on an auxiliary guide shaft  716  which passes through the axially aligned openings  714 A,  714 B in the legs  712 A,  712 B. The auxiliary guide shaft  716  is secured to the base  602  by a securing pin  716 A inserted into an traverse aperture  716 B formed at one end of the auxiliary guide shaft  716  ( FIG. 17 ). 
   The auxiliary guide shaft  716  also passes through a spring  717  which is coaxially mounted with the auxiliary guide  704 . The spring  717  spaces apart the auxiliary guide  704  from an interior side wall of the auxiliary recess  702 . The spring  717  is configured to help mitigate a shock applied to the second guide; when the auxiliary guide is struck by an ULD that is being loaded onto a cargo deck, the spring  717  helps absorb the impact. In one embodiment, the spring  717  is formed from an elastic material, such as polyurethane. In other embodiments, the spring  717  may be a compression spring. 
   The auxiliary guide  704  can occupy either an upright position ( FIG. 16 ) or a retracted position ( FIG. 17 ). A pair of torsion springs  718 A,  718 B are mounted on the auxiliary guide pin  716  between the legs  712 A,  712 B, via an auxiliary sleeve  720 . The back surface  710  of the auxiliary guide  704  is provided with a recess  722  into which ends  724 A,  724 B of the auxiliary springs  718 A,  718 B, respectively, protrude ( FIG. 17  and  FIG. 19 ). The torsion springs  718 A,  718 B bias the auxiliary guide  704  into the upright position of  FIG. 17 . 
   The front surface  706  of the auxiliary guide  704  is rearwardly angled from a forwardmost point  707 A near an inner portion of the base  602  to a rearwardmost point  707 B proximate a base edge  604 . Thus, the front surface  706  of the auxiliary guide  704  is angled in the same direction as the front side  557  of the wedge-shaped guide head  554  belonging to guide  522 . 
   The top surface  708  of the auxiliary guide  704  is provided with a latch recess  726 . The latch recess  726  is configured and dimensioned to receive the latch  728  of a release element  730  that is mounted in the floor of the auxiliary recess  702 . When the auxiliary guide is in the upright position of  FIG. 17  or  FIG. 19 , an operator may rotate the auxiliary guide  704 , against the biasing force of the auxiliary springs  718 A,  718 B and in the direction indicated by rotational arrow T ( FIG. 19 ), until the latch  728  is captured by the latch recess  726 . When the auxiliary guide  704  is in the retracted position of  FIG. 16  with the latch  728  captured in the latch recess  726 , an operator may manually press the spring loaded latch release  732  to withdraw the latch  728  from the latch recess  726 , and thereby allow the torsion springs  718 A,  718 B to return the auxiliary guide  704  to the upright position of  FIG. 17 . 
   The guide/restraint  600  is suitable for mounting near a doorway, such as a side doorway, of an air cargo main deck. The auxiliary guide  704 , and especially the spring  717  adjacent thereto, helps protect the guide/restraint  600  from high impact loads that may result when an ULD being loaded is not aligned properly as it enters the cargo hold. 
     FIG. 20  shows a partial layout of a Boeing 747 main air cargo deck  900 , depicting the centerline  902  of the cargo deck  900  and a 20 foot pallet  910  loaded along the centerline  902  and retained by a plurality of guides/restraints not unlike those seen in  FIG. 1 . In  FIG. 20 , the pallet  910  is shown as a rectangular outline defined by a pair of parallel long sides  912 ,  914 , a forward end  916  and an aft end  918 . 
   In one embodiment, the pallet  910  is mounted just aft of the wingbox area of the main cargo deck  900 . The wingbox area is an area of the cargo deck  900  which corresponds to the locations on either side of the fuselage where the aircraft&#39;s wings are attached. Thus, the wingbox area extends for an axial length along the cargo deck that more or less corresponds to the width of the wings where they attach to the fuselage. In the wingbox area, beneath the cargo deck, are a plurality of spaced apart floor beams, or joists, which extend longitudinally, or lengthwise, along the fuselage. Outside the wingbox area are a plurality of spaced apart weight-bearing floor beams, or joists, which extend transversely, or widthwise, to the fuselage. Generally speaking, the floor beams outside the wingbox area are able to sustain greater loads than the floor beams inside the wingbox area, and so the pallet  910  is preferably loaded outside the wingbox area. 
   On either side of the centerline  902  are a pair of axially extending seat tracks  904 A,  904 B. It is understood, however, that additional seat tracks and lock trays, not relevant to the present discussion, may also be present on the cargo deck  900 . In an outboard direction (i.e., in a direction away from the centerline  902  and towards the sides of the cargo compartment) from either seat track  904 A,  904 B is an axially extending roller tray  906 A,  906 B. The seat tracks  904 A,  904 B and the roller trays  906 A,  906 B are parallel to one another. Two parallel rows  920 ,  930  of guides/restraints extend parallel to, and on opposite sides of, the centerline  902 . The guides/restraints connect the seat tracks  904 A,  904 B to corresponding roller trays  906 A,  906 B, respectively. In the embodiment shown, the first row  920  includes guides/restraints  920 A,  920 B,  920 C,  920 D,  920 E,  920 F,  920 G, while the second row  930  includes guides/restraints  930 A,  930 B,  930 C,  930 D,  930 E,  930 F,  930 G. 
   It is understood that the various guides/restraints  920 A-G and  930 A-G are similar in construction to guide/restraint  100  described above insofar that each has coaxially mounted guides  122  and lockheads  124  on the outboard end. However, the shape and position of the gussets  220  in each of these guides/restraints  920 A-G and  930 A-G may differ from one to another so as to properly direct vertical loads, via the shear bosses  112  ( FIG. 1 ), directly into the aforementioned transversely extending, weight-bearing floor beams underlying the cargo deck  900  outside the wingbox area. Thus, in one embodiment, the guides/restraints  920 A-G and  930 A-G retaining the pallet  910  are mounted outside the wingbox area of the cargo deck  900 . 
   As seen in  FIG. 20 , the first, or “inboard”, ends  950  of these guides/restraints  920 A-G and  930 A-G connect to the seat tracks  904 A,  904 B, respectively, while their second, or “outboard”, ends  960  connect to the lock trays  906 A,  906 B, respectively, in a manner described above. Thus, while one or more types of fixation devices connect the first end of the guides/restraints  920 A-G and  930 A-G to a first retaining device (e.g., either the seat track or the lock tray), different fixation devices connect the second end of the guides/restraints  920 A-G and  930 A-G to the second retaining device (e.g., the other of the seat track or the lock tray). 
   In the embodiment of  FIG. 20 , the 20 foot pallet  910  is retained along the centerline  902  by a plurality of guides/restraints  920 A-G and  930 A-G that connect at a first end to a seat track  904 A,  904 B and at a second end to lock trays  906 A,  906 B, each of the guides/restraints  920 A-G and  930 A-G having a coaxially mounted guide and lockhead, the guide configured to guide a passing ULD and the lockhead configured to help retain the ULD. The guides/restraints ( 920 A-G and  930 A-G are mounted in the cargo deck  900  such that the inboard end  950  of each guide/restraint is closer to the centerline  902  than the outboard end  960  of that guide/restraint. In addition, the inboard end  950  of each guide/restraint is attached to a seat track  904 A,  904 B, while the outboard end  960  of each guide/restraint is attached to a lock tray  906 A,  906 B. 
   While  FIG. 20  shows a 20 foot pallet  910  loaded and retained along a centerline  902 , it is understood that standard size pallets of other lengths, such as a standard 16 foot pallet or a standard 10 foot pallet may likewise be loaded along the centerline  902 . For either a standard 16 foot pallet or a standard 10 foot pallet, a subset of the 14 guides/restraints  920 A-G and  930 A-G may be employed. For example, in one embodiment, to retain a standard 16 foot pallet along the centerline  902 , only six guides/restraints from each row  920 ,  930 , and in particular guides/restraints  920 A-F and  930 A-F may be used, guide/restraints  920 G and  930 G not being used. Similarly, to retain a standard 10 foot pallet along the centerline  902 , only four guides/restraints from each row  920 ,  920 , and in particular guides/restraints  920 C-F and  930 C-F may be used, guide/restraints  920 A,  920 B,  920 A,  920 G,  930 A,  930 B,  930 G being idle. In some embodiments, especially for the shorter pallets, additional restraints may be used to engage the pallet&#39;s forward end  916  and/or aft end  918 , to further secure the pallet. 
   In summary, then, the air cargo deck  900  has first and second rows  920 ,  930  extending parallel to, and on opposite sides of, the centerline  902 . Each row  920 ,  930  comprises a plurality of guides/restraints  920 A-G,  930 A-G, respectively. In the embodiment shown, the guides/restraints are mounted in the cargo deck  900  such that the first end  950  of a guide/restraint is closer to the centerline  902  than the second end  960  of that guide/restraint, the first end  950  being attached to a seat track and the second end  960  being attached to a lock tray. Finally, these guides/restraints are mounted outside the wingbox area of the cargo deck  902  where transversely extending floor beams provide adequate support for the loads applied by pallets. 
   A method for loading a standard size pallet  910  along the centerline  902  of an air cargo deck  900  in accordance with one embodiment of the present invention begins with providing the first and second rows  920 ,  930  of the guides/restraints  920 A-G,  920 A-G on either side of the centerline  902 , in the manner summarized above. Next, the standard size pallet  910  is positioned such that it straddles the centerline  902  with long sides  912 ,  914  of the pallet  910  overlying a portion of the base of at least some of the guides/restraints in each row  920 ,  930 . Finally, the lockheads of the guides/restraints over which the long sides  912 ,  914  of pallet  910  overlie must be rotated from the retracted position to the upright position, to thereby retain the standard size pallet  910  in position. It is understood that in some embodiments, the guides  122  of the guides/restraints that are being used in each row  920 ,  930  may also need to be rotated from the retracted position to the upright position, either prior to, or at the same time as, the lockheads  124 . The pallet  910  may thus be restrained without the use of straps, thus saving time in loading and unloading the aircraft. Prior to loading the pallet  910  onto the cargo deck  900 , an item of out-sized cargo (not shown) may be placed on pallet  910 . 
   One may modify existing main cargo decks of certain Boeing 747 air cargo planes so that they can accommodate centerline loading of pallets, such as pallet  910 , without the use of straps to tie down the pallet. The cargo decks on these certain planes are already equipped with first and second seat tracks  904 A,  904 B, respectively, extending parallel to the centerline  902  and positioned on either side thereof, and first and second lock trays  906 A,  906 B, respectively, extending parallel to the centerline  902  and positioned on either side thereof, each of the first and second lock trays  906 A,  906 B being spaced apart from a corresponding seat track  904 A,  904 B, respectively, and being farther from the centerline  902  than its corresponding seat track. Such a cargo deck may be modified by installing one row  920  comprising a first plurality of guides/restraints  920 A-G between the first seat track  904 A and the first lock tray  906 A, and installing a second plurality of guides/restraints  930 A-G between the second seat track  904 B and the second lock tray  906 B. Such a modification allows such a plane to carry standard size pallets that straddle the centerline, without the use of straps to tie down the pallet. As discussed above, in making these modifications, the guides/restraints would be installed outside the wing box area of the air cargo deck  900 , and more particularly, aft of the wingbox area. 
   In the foregoing description, the pallet  910  is retained by the guides/restraints  920 A-G,  920 A-G without the use of straps. However, in some embodiments, straps may be used in addition to the guides/restraints of the present invention. This provides the necessary flexibility to accommodate unusual loads, non-standard pallets and other ULDs. 
   While the present invention has been described herein above in connection with a plurality of aspects and embodiments, it is understood that these aspects and embodiments were presented by way of example with no intention of limiting the invention. Accordingly, the present invention should not be limited to any specific embodiment or aspect, but rather construed in breadth and broad scope in accordance with the recitation of the claims appended hereto.