Abstract:
An aircraft-side aircraft data retrieval system and method, comprising: a data storage device ( 14 ) located in a first location, for example a bay ( 8 ), in a aircraft ( 2 ) adapted to, during a flight, store data acquired during the flight; and wireless apparatus ( 18 ) comprising an antenna ( 28 ), at least the antenna ( 28 ) being located in a second location, for example an undercarriage bay, in the aircraft ( 2 ) that is different to the first location, the wireless apparatus ( 18 ) adapted to wirelessly transmit, after landing, the stored data to a ground-side data retrieval system ( 6 ); the second location ( 10 ) being a location that can have a closed or open configuration and which will be in the closed configuration for at least a majority of the flight and in the open configuration, for a purpose other than retrieving the stored data, after the aircraft ( 2 ) has landed.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention relates to the retrieval of data stored by an aircraft. The present invention relates in particular to, but is not limited to, retrieval of data acquired and stored by an aircraft during a flight. 
       BACKGROUND 
       [0002]    Conventionally, during a mission, data is acquired (and/or updated) and stored by a military aircraft. In some cases, such data is stored in a storage module in an electromagnetically sealed bay of the military aircraft, with the electromagnetically sealed bay having one or more electromagnetically sealed panels. Conventionally, after one or more missions are completed, the data is retrieved by removing the sealed panel and physically accessing the data storage module, which for example may include physically removing the data storage module, or one or more storage media of a storage module, from the aircraft. Removal and then replacement of the sealed panel can lead to increased turnaround and/or maintenance times. 
         [0003]    In the field of civilian aircraft, wireless communication of data between an aircraft and ground side equipment, whilst on the ground, is known. See for example U.S. Pat. No. 7,835,734. 
       SUMMARY OF THE INVENTION 
       [0004]    In a first aspect, the invention provides an aircraft-side aircraft data retrieval system, comprising: a data storage device located in a first location in an aircraft adapted to, during a flight, store data acquired during the flight; and wireless apparatus comprising an antenna, at least the antenna being located in a second location in the aircraft that is different to the first location, the wireless apparatus adapted to wirelessly transmit, after the aircraft has landed, the stored data to a ground-side data retrieval system; wherein: the second location is a location that can have a closed or open configuration and which will be in the closed configuration for at least a majority of the flight and in the open configuration, for a purpose other than retrieving the stored data, after the aircraft has landed; and when the second location is in the open configuration the second location is less electromagnetically sealed than the first location. 
         [0005]    The first location may be an electromagnetically sealed bay of the aircraft. 
         [0006]    The first location may be an avionics bay of the aircraft. 
         [0007]    The second location may be an undercarriage bay of the aircraft. 
         [0008]    The aircraft-side aircraft data retrieval system may further comprise apparatus adapted to provide a wireless bridge between the first location and the second location. 
         [0009]    The wireless apparatus may be adapted to wirelessly transmit, after the aircraft has landed, the stored data to a ground-side data retrieval system at a frequency in a range selected from the following ranges: (i) 50-330 GHz, (ii) 22-24 GHz. 
         [0010]    The frequency may be in the range of 50-70 GHz. 
         [0011]    The frequency may be in a range selected from the following ranges: (i) 50-70 GHz, (ii) 110-120 GHz, (iii) 170-190 GHz, (iv) 310-330 GHz, (v) 22-24 GHz. 
         [0012]    The system may be for use on a military aircraft and as such the data storage device may be located in a first location on a military aircraft. 
         [0013]    In a further aspect, the invention provides a ground-side aircraft data retrieval system, comprising: wireless apparatus adapted to wirelessly receive data acquired and stored by the aircraft during flight and transmitted after landing by the aircraft from a location in the aircraft that can have a closed or open configuration and which will be in the closed configuration for at least a majority of the flight and in the open configuration, for a purpose other than retrieving the stored data, after the aircraft has landed, using an aircraft-side data retrieval system according to any of the above aspects and options. 
         [0014]    The ground-side aircraft data retrieval system may be located in a hand-held terminal. 
         [0015]    In a further aspect, the invention provides an aircraft data retrieval system, comprising: an aircraft-side aircraft data retrieval system according to any of the above aspects and options; and a ground-side aircraft data retrieval system according to any of the above aspects and options. 
         [0016]    In a further aspect, the invention provides an aircraft-side aircraft data retrieval method, comprising: during a flight by an aircraft, storing data acquired during the flight in a storage device located in a first location in the aircraft; and after the aircraft has landed, wirelessly transmitting the stored data to a ground-side data retrieval system using an antenna located in a second location in the aircraft that is different to the first location; wherein: the second location is a location that can have a closed or open configuration and which will be in the closed configuration for at least a majority of the flight and in the open configuration, for a purpose other than retrieving the stored data, after the aircraft has landed; and when the second location is in the open configuration the second location is less electromagnetically sealed than the first location. 
         [0017]    In a further aspect, the invention provides an aircraft data retrieval method, comprising performing an aircraft-side aircraft data retrieval method according to the above aspect; and wirelessly receiving stored data transmitted during the performance of the aircraft-side aircraft data retrieval method according to the above aspect. 
         [0018]    In a further aspect, the invention provides a program or plurality of programs arranged such that when executed by a computer system or one or more processors it/they cause the computer system or the one or more processors to operate in accordance with the above aspects and options. 
         [0019]    In a further aspect, the invention provides a machine readable storage medium storing a program or at least one of the plurality of programs according to the above aspect. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0020]      FIG. 1  is a schematic block diagram of an embodiment of a data retrieval system for use with an aircraft; 
           [0021]      FIG. 2  is a block diagram showing further details of an undercarriage bay aircraft-ground link module and a ground side wireless system of the data retrieval system of  FIG. 1 ; 
           [0022]      FIG. 3  is a schematic block diagram of a further embodiment of a data retrieval system for use with an aircraft; 
           [0023]      FIG. 4  is a process flowchart showing certain steps of an embodiment of a data retrieval process; and 
           [0024]      FIG. 5  is a process flowchart showing certain steps of a further embodiment of a data retrieval process. 
       
    
    
     DETAILED DESCRIPTION 
       [0025]      FIG. 1  is a schematic block diagram of an embodiment of a data retrieval system  1  for use with a military aircraft  2 . 
         [0026]    In this embodiment the data retrieval system  1  comprises an aircraft-side data retrieval system  4  and a ground side data retrieval system  6 . 
         [0027]    In this embodiment the aircraft  2  comprises an undercarriage bay  10  and a further bay  8 . As will be described below, the data to be retrieved is stored in the further bay  8 . The further bay  8  comprises an external aircraft panel  9  that is electromagnetically sealed. By way of example, in this particular embodiment the further bay  8  is an avionics bay  8 . 
         [0028]    The undercarriage bay  10  has an external panel  9  that is electromagnetically sealed when the undercarriage bay  10  is closed. In  FIG. 6  the aircraft  2  is on the ground with the undercarriage bay  10  open so that its undercarriage  12  is effective. This is the primary reason the undercarriage bay  10  has been opened. However, as will be described in more detail below, use is made of the secondary aspect that as a result of being open, the undercarriage bay  10  is no longer electromagnetically sealed. 
         [0029]    In this embodiment the aircraft-side data retrieval system  4  comprises an data storage module  14  and an avionics bay wireless system  16 . The data storage module  14  and the avionics bay wireless system  16  are operably coupled to each other and both are located in the avionics bay  8 . 
         [0030]    In this embodiment the aircraft-side data retrieval system  4  further comprises an undercarriage bay wireless system  18  located in the undercarriage bay  10 . The undercarriage bay wireless system  18  comprises an undercarriage bay wireless bridge module  20  and an undercarriage bay aircraft-ground link module  22 . The undercarriage bay wireless bridge module  20  and the undercarriage bay aircraft-ground link module  22  are operably coupled to each other. 
         [0031]    In this embodiment the ground side data retrieval system  6  comprises a ground side wireless system  24  located in a hand-held terminal  26 . 
         [0032]    In this embodiment, each of the avionics bay wireless system  16 , the undercarriage bay wireless bridge module  20 , the undercarriage bay aircraft-ground link module  22 , and the ground side wireless system  24  comprises a respective antenna  28 . The avionics bay wireless system  16  and the undercarriage bay wireless bridge module  20  are operably coupled together by a wireless bridge link  30  provided via their respective antennas  28 . The undercarriage bay aircraft-ground link module  22  and the ground side wireless system  24  are operably coupled together by a data retrieval system wireless link  32  provided via their respective antennas  28 . 
         [0033]    The above arrangement is described in more detail as follows. 
         [0034]    In this embodiment, data is acquired on the aircraft  2  during a flight and stored at the data storage module  14 . The data storage module  14  may be implemented in any conventional fashion, including one or more processors and one or more storage media. Additionally, in this embodiment, the data storage module  14  comprises a conventional input and output arrangement. 
         [0035]    The data storage module  14  is operably coupled (in this embodiment via a hard-wired link) to the avionics bay wireless system  16 . In conventional arrangements, after the aircraft lands after a mission, the avionics bay  8  would be opened and a conventional data storage module would be physically coupled to a ground side data retrieval system. In contrast, in this embodiment, a wireless link is established between the data storage module  14  and a ground side data retrieval system  6  (the latter comprises the hand held terminal  26  in this embodiment), and the data is retrieved from the data storage module  14  over the wireless link. In this embodiment, the wireless link comprises a chain comprising three wireless nodes. The first node is the avionics bay wireless system  16 . 
         [0036]    The second node is the undercarriage bay wireless system  18 , which is located in the undercarriage bay  10 . A wireless bridge link  30  is provided between the avionics bay wireless system  16 , via its antenna  28 , and the undercarriage bay wireless bridge module  20  (in particular its antenna  28 ) of the undercarriage bay wireless system  18 . In this embodiment the wireless bridge link  30  operates at a frequency around of approximately 60 GHz, although this need not be the case in other embodiments. 
         [0037]    The undercarriage bay wireless bridge module  20  is operably coupled (in this embodiment via a hard-wired link) to the undercarriage bay aircraft-ground link module  22 . 
         [0038]    The third node is the ground side wireless system  24 , which is located in the hand held terminal  26 . A data retrieval system wireless link  32  is provided between the undercarriage bay aircraft-ground link module  22 , via its antenna  28 , and the ground side wireless system  24  (in particular its antenna  28 ). In this embodiment the data retrieval system wireless link  32  operates at a frequency of approximately 60 GHz, although this need not be the case in other embodiments. 
         [0039]    In operation, data acquired or updated during the flight is stored at the data storage module  14 . After the aircraft  2  has landed, the hand held terminal is brought into a position that allows adequate wireless transmission/reception between the undercarriage bay aircraft-ground link module  22  and the ground side wireless system  24 . Since in this embodiment the wireless frequency employed is approximately 60 GHz, at which value there is relatively high atmospheric attenuation, this range is about 5 metres maximum. This provides good security against eavesdropping. 
         [0040]    The undercarriage bay  10  is an example of a part of the aircraft that will normally be in a closed state during most of the flight, thereby typically providing part of an in-flight sealed wireless barrier, but which is in an opened state for other reasons after the aircraft has landed. 
         [0041]    Consequently, one advantage that tends to be provided by virtue of locating the last aircraft-side node of the wireless chain in such a part of the aircraft is that the provision of the data retrieval system does not affect the wireless containment properties of the aircraft in flight (i.e. the external electromagnetic sealing is not interrupted during flight, including not at all during the whole flight for the avionics bay, and for the undercarriage bay interruption only occurring close to landing when the undercarriage bay is opened in preparation for landing). 
         [0042]    Another advantage that tends to be provided by virtue of locating the last aircraft-side node of the wireless chain in such a part of the aircraft is that there is no need to open any panel of the aircraft just for the sake of allowing higher wireless connectivity on the ground, since the undercarriage bay is already open (i.e. the extent to which wireless transmission from the undercarriage bay will be attenuated is reduced by virtue of the bay being open). For example, it is noted that the avionics bay  8  does not need to be opened, with consequential delays regarding opening and later re-establishing, the electromagnetic sealing, despite this being where the data storage module  14  (and hence the stored data) is located. 
         [0043]    The avionics bay wireless system  16  and the undercarriage bay wireless bridge module  20  together provide a wireless bridge (in particular the wireless bridge link  30 ) enabling data to be passed between the data storage module  14  and the undercarriage bay aircraft-ground link module  22 . An advantage of operably coupling the data storage module  14  and the undercarriage bay aircraft-ground link module  22  together in this way (i.e. by provision of a wireless bridge) that tends to be provided is that there is no need to provide a hard-wired link, avoiding for example a need to undermine the electromagnetic integrity of the avionics bay  8  that may have particularly high levels of integrity of sealing of its enclosure. 
         [0044]      FIG. 2  is a block diagram showing further details of the undercarriage bay aircraft-ground link module  22  and the ground side wireless system  24 . Where applicable the same reference numerals are used to refer to the same elements as shown in  FIG. 1 . Also shown in  FIG. 2  is the data retrieval system wireless link  32 . 
         [0045]    In this embodiment the undercarriage bay aircraft-ground link module  22  and the ground side wireless system  24  are the same as each other. Each comprises an Ethernet digital input/output  60 , a wireless modem  62 , a circulator  64 , a reception branch  66 , a transmission branch  68 , a transmission/reception diplexer  70 , an antenna  28  (which in this embodiment is a horn antenna), and a window that is transparent to the wireless frequency employed (which in this embodiment is approximately 60 GHz). The reception branch  66  comprises an In-phase and Quadrature (IQ) splitter  72  and a reception module  74  coupled to each other by two separate couplings, one for Q and one for I. The transmission branch  68  comprises an IQ splitter  76  and a transmission module  78  coupled to each other by two separate couplings, one for Q and one for I. 
         [0046]    In this embodiment the wireless modem  62  operates at a frequency of 2.4 GHz, but other frequencies are possible, one example being in the range 1 to 6 GHz. 
         [0047]    The Ethernet digital input/output  60  is coupled to the wireless modem  62 . The wireless modem  62  is further coupled to the circulator  64 . The circulator  64  is further coupled to the reception branch  66  and the transmission branch  68 , more particularly to the IQ splitter  72  of the reception branch  66  and to the IQ splitter  76  of the transmission branch  68 . The reception branch  66 , more particularly the reception module  74  of the reception branch  66 , is coupled to the transmission/reception diplexer  70 . The transmission branch  68 , more particularly the transmission module  78  of the transmission branch  68 , is coupled to the transmission/reception diplexer  70 . The transmission/reception diplexer  70  is further coupled to the horn antenna  28 . Other types of antenna could also be used to provide different beamwidths and antenna gains. 
         [0048]    The data retrieval system wireless link  32  is provided between the respective antennas  28  of the undercarriage bay aircraft-ground link module  22  and the ground side wireless system  24 , including passing through the respective 60 GHz transparent windows  80 . These allow the 60 GHz signals to pass through the sealed boxes in which 22 and 24 are located in this embodiment. 
         [0049]    In this embodiment the Ethernet digital input/output  60  of the undercarriage bay aircraft-ground link module  22  is coupled (over a hard wired link) to an Ethernet digital input/output of the undercarriage bay wireless bridge module  20 . 
         [0050]    In this embodiment the Ethernet digital input/output  60  of the ground side wireless system  24  is coupled to any suitable end-use arrangement. For example, the Ethernet digital input/output  60  may be coupled to one or more storage media (not shown) comprised by the hand held terminal  26 . The one or more storage media may removable or fixed or one or more of each. 
         [0051]    In operation, in this embodiment the each of the undercarriage bay aircraft-ground link module  22  and the ground side wireless system  24 , and the arrangement of  FIG. 2  as a whole, operates as follows. 
         [0052]    At the request of the operator in control of the ground side wireless system  24 , a command is issued on a data terminal connected to the Ethernet digital input/output  60  to download maintenance data from the data storage module  14 . This instruction is transmitted from the ground side wireless system  24  via the data retrieval system wireless link  32  to the undercarriage bay aircraft-ground link module  22 . The wireless signal is demodulated and connected by cable to the undercarriage bay wireless bridge module  20 . The signal is then modulated onto a 60 Ghz carrier and then re-transmitted by the undercarriage bay wireless bridge module  20  to the receiver contained within the avionics bay wireless system  16 . The Ethernet digital output from avionics bay wireless system  16  is received by the data storage module  14  over the Ethernet cable connection. On reception the data storage module  14  responds to the request to download data and transmits the data to the avionics bay wireless system  16  on the Ethernet cable connection. The data is then modulated onto a 60 GHz carrier and transmitted by the avionics bay wireless system  16  over the wireless bridge link  30  to the receiver located in the undercarriage bay wireless bridge module  20 . The wireless data is then demodulated and the Ethernet data is electrically connected to the transmitter in the undercarriage bay aircraft-ground link module  22 , where the Ethernet data is modulated onto a 60 GHz carrier for transmission over the data retrieval system wireless link  32  to the ground side wireless system  24 . The data terminal connected to the Ethernet digital input/output  60  then receives the requested data. 
         [0053]    The wireless modems  62  are used to convert the Ethernet digital data on port  60  to a suitable modulation for transmission over the wireless links. Coded Orthogonal Frequency Division Multiplexing modulation and coding is one preferred example in order to minimise the impact of the multiple reflections of the wireless signals  30  and  32  encountered in the avionics bay  8  and undercarriage bay  10  areas. 
         [0054]    Wireless bridging link  30  removes the need to install additional cabling and hence the data download system can be implemented with minimum modification to the airframe. 
         [0055]    In the above embodiments, the data storage module  14  and the undercarriage bay wireless system  18  are operably coupled together by provision of the above described wireless bridge. However, this need not be the case, and in other embodiments the data storage module  14  and the undercarriage bay aircraft-ground link module  22  may be coupled together by provision of any other suitable type of link or operable coupling. For example, they may be coupled together by provision of one or more hard-wired links. 
         [0056]      FIG. 3  is a schematic block diagram of one such further embodiment of a data retrieval system  1  for use with the aircraft  2 . Except where stated otherwise below or where consequently not possible/applicable, the data retrieval system  1  of this further embodiment ( FIG. 3 ) comprises the same elements, operating the same way, as described for the above embodiments with reference to  FIGS. 1 and 2  (and where applicable the same reference numerals are used in  FIG. 3  to refer to the same elements as shown in  FIGS. 1 and 2 ). 
         [0057]    In this embodiment the data retrieval system  1  comprises an aircraft-side data retrieval system  4  and a ground side data retrieval system  6 . 
         [0058]    In this embodiment the aircraft  2  comprises an undercarriage bay  10  and a further bay  8 . As will be described below, the data to be retrieved is stored in the further bay  8 . The further bay  8  comprises an external aircraft panel  9  that is electromagnetically sealed. By way of example, in this particular embodiment the further bay  8  is an avionics bay  8 . 
         [0059]    The undercarriage bay  10  has an external panel  9  that is electromagnetically sealed when the undercarriage bay  10  is closed. In  FIG. 3  the aircraft  2  is on the ground with the undercarriage bay  10  open so that its undercarriage  12  is effective. This is the primary reason the undercarriage bay  10  has been opened. However, as will be described in more detail below, use is made of the secondary aspect that as a result of being open, the undercarriage bay  10  is no longer electromagnetically sealed. 
         [0060]    In this embodiment the aircraft-side data retrieval system  4  comprises an data storage module  14  located in the avionics bay  8 . 
         [0061]    In this embodiment the aircraft-side data retrieval system  4  further comprises an undercarriage bay wireless system  18  located in the undercarriage bay  10 . The undercarriage bay wireless system  18  comprises an undercarriage bay aircraft-ground link module  22 . 
         [0062]    In this embodiment the ground side data retrieval system  6  comprises a ground side wireless system  24  located in a hand-held terminal  26 . 
         [0063]    In this embodiment, each of the undercarriage bay aircraft-ground link module  22  and the ground side wireless system  24  comprises a respective antenna  28 . 
         [0064]    In this embodiment the data storage module  14  is operably coupled via the hard-wired link  130  to the undercarriage bay aircraft-ground link module  22 , which is located in the undercarriage bay  10 . A data retrieval system wireless link  32  is provided between the undercarriage bay aircraft-ground link module  22 , via its antenna  28 , and the ground side wireless system  24  (in particular its antenna  28 ). In this embodiment the data retrieval system wireless link  32  operates at a frequency of approximately 60 GHz, although this need not be the case in other embodiments. 
         [0065]    The above arrangement is described in more detail as follows. 
         [0066]    In this embodiment, data is acquired on the aircraft  2  during a flight and stored at the data storage module  14 . The data storage module  14  may be implemented in any conventional fashion, including one or more processors and one or more storage media. Additionally, in this embodiment, the data storage module  14  comprises a conventional input and output arrangement. 
         [0067]    In conventional arrangements, after the aircraft lands after a mission, the avionics bay  8  would be opened and a conventional data storage module would be physically coupled using an Ethernet digital cable connection to a ground side data retrieval system. In contrast, in this embodiment, the data is retrieved from the data storage module  14  via the hard-wired link  130  and the data retrieval system wireless link  32 . 
         [0068]    In operation, data acquired or updated during the flight is stored at the data storage module  14 . After the aircraft  2  has landed, the hand held terminal  26  is brought into a position that allows adequate wireless transmission/reception between the undercarriage bay aircraft-ground link module  22  and the ground side wireless system  24 . Since in this embodiment the wireless frequency employed is approximately 60 GHz, this range is about 5 metres maximum. This provides good security against eavesdropping. 
         [0069]    The undercarriage bay  10  is an example of a part of the aircraft that will normally be in a closed state during most of the flight, thereby typically providing part of an in-flight sealed wireless barrier, but which is in an opened state for other reasons after the aircraft has landed. Consequently, one advantage that tends to be provided by virtue of locating the last aircraft-side node of the wireless chain in such a part of the aircraft is that the provision of the data retrieval system has a reduced or minimised extent of lowering the wireless containment properties of the aircraft in flight. Another advantage that tends to be provided by virtue of locating the last aircraft-side node of the wireless chain in such a part of the aircraft is that there is no need to open any panel of the aircraft just for the sake of allowing wireless connectivity on the ground, since the undercarriage bay is already open (i.e. the extent to which wireless transmission from the undercarriage bay will be attenuated is reduced by virtue of the bay being open). For example, it is noted that the avionics bay  8  does not need to be opened, with consequential delays regarding opening and later re-establishing, the electromagnetic sealing, despite this being where the data storage module  14  (and hence the stored data) is located. 
         [0070]    In this embodiment the undercarriage bay aircraft-ground link module  22  and the ground side wireless system  24  are the same as described above with reference to  FIG. 2 . 
         [0071]    In this embodiment the Ethernet data input/output  60  of the undercarriage bay aircraft-ground link module  22  is coupled via the hard-wired link  30  to the Ethernet data input/output of the data storage module  14 . 
         [0072]    In this embodiment the Ethernet data input/output  60  of the ground side wireless system  24  is coupled to any suitable end-use arrangement. For example, the Ethernet input/output  60  may be coupled to one or more storage media (not shown) comprised by the hand held terminal  26 . The one or more storage media may removable or fixed or one or more of each. 
         [0073]    In the above embodiments, an aircraft-ground link module  22  is located in the undercarriage bay, i.e. the undercarriage bay is the selected bay for use as a bay or other enclosure that will give less attenuation after it is open, and where that bay will also be open or opened, when the aircraft  2  is on the ground, for other reasons. However, in other embodiments, a different bay or enclosure of the aircraft  2  other than the undercarriage bay  10  may be employed (as a bay that will give less attenuation after it is open), where that other bay will also be open or opened, when the aircraft  2  is on the ground, for other reasons. 
         [0074]    In all the above embodiments the undercarriage bay aircraft-ground link module  22  and the ground side wireless system  24  are of the same type, design and specification as each other. However, this need not be the case, and in other embodiments their types and/or design and/or specifications may be different to each other. In other embodiments even when one or more of these characteristics are the same, they may be different to those described above. Examples of different possibilities include the following. 
         [0075]    In the above embodiments the input/output  60  is Ethernet digital signals providing a bi-directional transmission path for both data and handshaking for acknowledging receipt of a data packet. In other embodiments, a simplified single direction transmission system may be implemented with transmission from the data storage module  14  to the hand held terminal  26 . The data download transmission would be initiated by a different method (any suitable conventional method) compared to that described above as the initial request from the hand held terminal  26  to the data storage module  14  would not be supported with a uni-directional link. 
         [0076]    In those of the above embodiments that include a wireless bridge, the wireless elements providing the wireless bridge, i.e. the avionics bay wireless system  16  and the undercarriage bay wireless system  18 , are both of the same type, design and specification as each other and also of the same type, design and specification as the undercarriage bay aircraft-ground link module  22  and the ground side wireless system  24 . However, this need not be the case, and in other embodiments one or more of these characteristics of one or both of the wireless elements providing the wireless bridge may be different to each other and/or different to those of one or both of the undercarriage bay aircraft-ground link module  22  and the ground side wireless system  24 . In the above embodiments, a 60 GHz transmission frequency has been used for the wireless bridge link  30  and the data retrieval system wireless link  32 . In other embodiments a different frequency may be used for the wireless bridge link  30  compared to the data retrieval system wireless link  32 . Also different modulation techniques may be adopted for the data retrieval system wireless link  32  compared to the wireless bridge link  30 , for example making use of any reduced multipath conditions in the undercarriage bay  10  compared to the avionics bay  8 . 
         [0077]    More generally, by use of any of any appropriate arrangements of apparatus, including the different embodiments of apparatus described above and including the options and alternative possibilities discussed in relation thereto, the following embodiments of data retrieval processes may be implemented. 
         [0078]      FIG. 4  is a process flowchart showing certain steps of an embodiment of a data retrieval process. 
         [0079]    At step s 2 , acquired data is stored in the avionics bay  8  during flight. In this embodiment the data is stored at the data storage module  14 . 
         [0080]    At step s 4 , during the approach for landing, the undercarriage bay  10  is opened. This reduces the extent to which later wireless transmission from the undercarriage bay  10  will be attenuated. In this embodiment this step is of course performed before the aircraft  2  lands. However, in other embodiments, a different bay or enclosure of the aircraft  2  other than the undercarriage bay  10  will be employed (as a bay that will give less attenuation after it is open), where that other bay will also be open or opened when the aircraft  2  is on the ground, for other reasons. If this is a bay that does not need to be opened until after the aircraft  2  is on the ground, then a step equivalent to s 4  (i.e. opening the relevant bay) may instead be performed after landing rather than before (i.e. after step s 6 ). 
         [0081]    Returning to the embodiment shown in  FIG. 4 , at step s 6  the aircraft  2  lands. 
         [0082]    Thereafter, when the aircraft  2  is stationery, steps s 8  and s 10  are performed as follows. 
         [0083]    At step s 8 , the stored data is transmitted over a wireless bridge link  30  provided by a wireless bridge from the avionics bay  8  to the undercarriage bay  10 . In this embodiment this step is performed by the avionics bay wireless system  16  and the undercarriage bay wireless system  18 , but this need not be the case, and in other embodiments other apparatus may be used. 
         [0084]    At step s 10 , the stored data is transmitted from the undercarriage bay  10  to a ground side system. In this embodiment this step is performed by the undercarriage bay wireless system  18  and, as the ground side system, the ground side wireless system  24 . However, this need not be the case, and in other embodiments other apparatus may be used. 
         [0085]    In other embodiments, step s 8  and/or step s 10  may instead be performed when the aircraft  2  is taxiing, or may instead be performed over a period of time in which for part of that period of time the aircraft  2  is stationery and for part of that period of time the aircraft  2  is taxiing. 
         [0086]      FIG. 5  is a process flowchart showing certain steps of a further embodiment of a data retrieval process. 
         [0087]    At step s 2 , acquired data is stored in the avionics bay  8  during flight. In this embodiment the data is stored at the data storage module  14 . 
         [0088]    At step s 4 , the undercarriage bay is opened. This reduces the extent to which later wireless transmission from the undercarriage bay  10  will be attenuated. The discussion above regarding step s 4  with reference to  FIG. 4  (regarding alternative bays and whether before or after landing) also applies to step s 4  in this embodiment. 
         [0089]    At step s 6  the aircraft  2  lands. 
         [0090]    Thereafter, when the aircraft  2  is stationery, steps s 9  and s 10  are performed as follows. 
         [0091]    At step s 9 , the stored data is forwarded from the avionics bay  8  to the undercarriage bay  10  over a hard-wired link  130 . In this embodiment this step is performed by the data storage module  14  and the undercarriage bay wireless system  18  via the hard-wired link  130 , but this need not be the case, and in other embodiments other apparatus may be used. 
         [0092]    At step s 10 , the stored data is transmitted from the undercarriage bay  10  to a ground side system. In this embodiment this step is performed by the undercarriage bay wireless system  18  and, as the ground side system, the ground side wireless system  24 . However, this need not be the case, and in other embodiments other apparatus may be used. 
         [0093]    In other embodiments, step s 9  and/or step s 10  may instead be performed when the aircraft  2  is taxiing, or may instead be performed over a period of time in which for part of that period of time the aircraft  2  is stationery and for part of that period of time the aircraft  2  is taxiing. 
         [0094]    In the above embodiments the wireless links are provided at a frequency of approximately 60 GHz, which has a relatively high extent of atmospheric attenuation. A preferred frequency range is 50-70 GHz. A more preferred frequency range is 55-65 GHz. 
         [0095]    In other embodiments the frequency may be at other frequency ranges that are not within the range 50-70 GHz, but which are instead in the vicinity of other frequency values that display a relatively high extent of atmospheric attenuation. Preferred ranges include, for example, 22-24 GHz, 110-120 GHz, 170-190 GHz, 310-330 GHz, or more generally 50-330 GHz. 
         [0096]    However, the frequency need not be at a value that has a relatively high extent of atmospheric attenuation, and in other embodiments other frequencies outside any of the above mentioned preferred ranges may be used. 
         [0097]    When more than one aircraft is to be provided with the above described data retrieval systems  1 , then different aircraft may be allocated different frequencies for their respective data retrieval system wireless links. Optionally this may also be the case, in those embodiments with a wireless bridge, for their respective wireless bridge links  30 . In some embodiments, use of 60 GHz or higher frequencies offers a wide bandwidth so that multiple non interfering channels can be accommodated. 
         [0098]    In the above embodiments, during flight, data is stored at the data storage module  14 . In other embodiments, other apparatus may be provided in addition to the data storage module  14  and take part in the activity of storing the data. For example, one or more additional processors and/or one or more separate storage media may be used. In yet further embodiments, other apparatus may be used instead of the data storage module, for example other types of processors and/or other separate storage media. In those embodiments where more than one apparatus is used, one or more of them may be located in different parts of the aircraft compared to the others. Indeed, in yet further embodiments, all the relevant apparatus may be located in a region of the aircraft other than a bay or compartment that is electromagnetically sealed in its entirety, for example in one that is at least sealed relative to the outside of the aircraft even if not sealed relative to one or more other regions inside the aircraft. 
         [0099]    More generally, apparatus, including the systems and modules described above, and other apparatus, including apparatus for implementing the above described processes, may be provided by configuring or adapting any suitable apparatus, for example one or more computers or other processing apparatus or processors, and/or providing additional modules. The apparatus may comprise a computer, a network of computers, or one or more processors, for implementing instructions and using data, including instructions and data in the form of a computer program or plurality of computer programs stored in or on a machine readable storage medium such as computer memory, a computer disk, ROM, PROM etc., or any combination of these or other storage media.