AIR TO AIR TACAN DME TEST 27 JANUARY 1967

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Document Number (FOIA) /ESDN (CREST): 
CIA-RDP71B00399R000300160001-9
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RIPPUB
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S
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19
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December 16, 2016
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September 1, 2004
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1
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Publication Date: 
January 27, 1967
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REPORT
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Approved For Release 2005/04/21 : CIA-RDP71B00399R000300160001-9 SECRET DME TEST USAF review(s) completed. 27 January 1967 SECRET Approved For Release 2005/04/21 : CIA-RDP71B00399R000300160001-9 25X1 25X1 Approved For Release 2005/04/21 : CIA-RDP71B00399R000300160001-9 Approved For Release 2005/04/21 : CIA-RDP71B00399R000300160001-9 Approved For Release P71B00399R000300160001-9 SUMMARY During the last six months-of?1966.several?.incidents of range.errors ?were . reported - in -the Air-to Air ?TACAN `install- ed in the A-12 and P-101"#2660 In all cases the-indicated ranges were -greater than actual range when the'error appear- ed. Aninvestigation was initiated;followed?by a, test plan to determine the cause of the error and-tosolve.-the problem if possible. It was theorizedthatthe range errors were caused by signals reflecting off the ground. A KC-135 tanker was instrumented :to prove'or-disprove this theory and an F-101 equipped with' an Air',t?o Air :TACAN was used as the receiver,.,:' The test proved.that the ,-theory was correct. Eliminating the use-of the tanker lower antenna greatly reduces the"-frequency 'of occurrence. 'This 'coupled with TACAN alignment" checks and the'adoption of-'various procedures to avoid,known'interference-problems-.,should'result in DME reli- ability and accuracy comparable'to=that achieved by "accepted" rendezvous -aids. Pending,additional experience pilots will be briefed that the .possibility "off:.a DME error does exist; present procedures which,require 10Mft-~of altitude separ- ation until the-tanker is-acquired?visually will be continued. I SECRET Approved For Release 2005/04/21 : CIA-RDP71B00399R000300160001-9 Approved For Release 2GW&N71B00399R000300160001-9 AML I -TABLE . OF, -CONTENTS . 1 Cover Page Foreword. . . . . . . . Summary . . . . Table of Contents . . . Page . . . . . . .? . . . . iii Introduction. . . . . . . . . . Objectives. . . . . . . . . . . . 1&2 Review and Approval . . . . ; . . .. 3 Distribution List . . . . . . . . . . . . . Attachment 1 (10 Pages) Description:of.Equipment Test Item Test Instrumentation Support Equipment Test Methods-&,Limitations Test Procedures Data Collection :& Reduction Accuracy of Data Test Results Conclusions Recommendations iii SECRET Approved For Release 2005/04/21 : CIA-RDP71B00399R000300160001-9 25X1 25X1 1 Approved For Release 2tR71B00399R000300160001-9 INTRODUCTION. 1. Air to Air?TACAN is',used as a.rendezvous aid for. the pur- poses of refueling the "Ai-12 , with a KC-115 -tanker. All of the KC-'s at Beale Air Force Base and all of the A-1225X I Iare equip p it''to Air ?TACAN. In addit one one o he F-IQl's is also equipped with an Air to Air TACAN. During ren evous, range information is dis- played to the A-12 pilot In'two ways: (1) The ARC-50 (2) Air to Air,TACAN. Should the ARC-50 range feature fail, then TACAN is the only means 'by which the A-12 pilot can obtain information regarding tanker/receiver range separation,. The KC-135 also has a radar transmitter/receiver to display both range and azimuth information.. 2. There is no doubt that range information is critical-to the tanker and receiver. During IFR conditions, lack of range information constitutes a termination of the rendezvous9 and an error in range information constitutes a safety of flight item. Upon the report of range errors in the TACAN a test was immediately initiated to investigate and solve the problem if.possible. 3. The cause of the range errors was thought to be associated with ,multipath signals. That is, when either the tanker's -TACAN or the receiver's'TACAN transmits the signal.travels directly and indirectly 'to the other aircraft. The indirect path,is a reflection off the ground and is consequently longer than the direct path. If the TACAN locks on to the indirect signal a greater than, actual range will be indicated. 'OBJECTIVES 4. The objectives 'of the'tes.t were to prove or disprove the theory that multipath reflections are causing the range errors, and to develop solutions to the problem if possible. RESULTS & CONCLUSIONS ..5. See the attached report for Description of the Equipment, Test Methods and Limitations, Test Results and Conclusions. How- ever, one comment. needs'to be.-added in the conclusions. That SECRET Approved For Release 2005/04/21 : CIA-RDP71B00399R000300160001-9 Approved For Release .6nULP_QPZ B00399R000300160001-9 is, a new type of Air-to Air >TACAN,with ,azimuth and range information will.be installed in the- .A-12 aircraft within ?a few months. Because of this -fact no-major ,modifications to the present equipment were recommended. We agree with the recommendations presented in the attached report not only because they will decrease the--frequency of range errors with the present equipment, but because most of them are sound procedures even if the range problem did not exist. The reliability of future Air to Air-TACAN equipment will benefit from the adopted recommendations. SECRET Approved For Release 2005/04/21 : CIA-RDP71B00399R000300160001-9 Approved For Release 2005/04/21 : CIA-RDP71B00399R000300160001-9 SECRET REVIEW AND APPROVAL. PREPARED BY: REVIEWED BY: REVIEWED BY: REVIEWED BY: REVIEWED BY: APPROVED BY: SECRET Approved For Release 2005/04/21 : CIA-RDP71B00399R000300160001-9 Approved For Release 2005/04/21 : CIA-RDP71B00399R000300160001-9 Si CRET ~ DISTRIBUTiON-LISS 25X1 UNIT Copies Commander DCO DCM DCOE 1 25X1 Project Headquarters ! SECRET 1 l Approved For Release 2005/04/21 : CIA-RDP71B00399R000300160001-9 ADVANCED DEVELOPMENT PROJECTS BUR B Aff.$ ...CAI.IPO R N 1 A REPORT NO. $P-1148 DATE 12-22-66 COPY NO.. Approved For Release 2005/04/21: CIA-RDP71B00399R000300160001-9 Configuration of aircraft involved in TACAN flight test. A. KC-135 1. ABBN-21 TACAN ability only a G p c a. A/ b. Gives range and bearing information from a ground station to th p e c. Can utilize one of two antennas. One located on and one located on the bbtton of the fuselage. can range only from another aircraft. c. Can utilize one of two antennas separately or can auto- matically switch back and forthebetween the two. One antenna is located on the top, the other on the bottom of the fuselage. 2. ARN-52 `ACAN a. A/G and A/A capability b. Gives range and bearing-information from aground station APX-25 IFF a. Normal IFF system utilizing one antenna located on the bottom of the fuselage. B. F-101 1.. AM-11-52V TACAN a. Temporary installation using one antenna the bottom.of the fuselage. 28 November 1966 2. Circuits . that- were monitored'on the tanker's TACAN unit.. a . Video output b. AGC voltage, c. Incoming.reply pulses: d. Antenna switching voltage B. Original condition of TACAN units received from KC-135 said F-101 1. S/N Q:-27 (tanker): Antenna. switching module inoperative. 16.5 DB signal rejection. Bearing flag pulls on course bearing only. 2. S/N (-28 (tanker): No A/A AGC which results in no rejection. Unit generally in very poor shape. 3. S/N ALT 350 (F-iOl): No A/A AGC. 1SgCRET Approved For Release 2005 B00399R000300160001-9 Approved For Release 2005/04/ 99 R000300`1,6;1001-9 1 - ... ? - . - . SP 411. +8 Page 2 of . III 29 November 1966 A. Preliminary 1. 2. 3. Installed units in tanker and checked same. Installed test equipment in tanker. Briefing for tanker and F-101 personnel. D. Condition of TACAN units prior to flight 1. S/N QK-27: No AGC, hence no rejection - instrumented 2. S/N A2,17,1805: Brand new unit received from Stewart Warner via Depot. Rejection was 14 DR -tsistrumented 3. S/.11, Q.-28: Reset for 15 DD rejection - spare. 4. S/I; ALA'-350: Remained the same - no rejection as unit was received originally from depot for the F-101 in this condition. C. Aircraft Involved in tests 1. F-101 (56-6291) 2. KC-135 (58-095) D. Test flight 1. Made normal TACAN rendezvous with Article 131 a. Multipaths were not noticed at this time as equipment was being set up after tanker take off. 2. Flight plan was followed with the F-101 during the first rendezvous. jFlight plan and test schedule published by a. Multipaths were very prevalent a good portion of the time b. Multipaths were apparently. approx. 30 miles. Doesn't seem to be a problem until 15-20 miles. At this point the multipath signal is approximately the same strength as.the direct signal.. c. F-101 obtained. high readings of two (2).miles?at.lapprox:' 10 miles down to-7 miles; at this.point the' -F-101, bro)se'`: lock and immediately locked on to the proper 'signal No further errors. were experienced during'-this rendezvous. 3. Deviated from flight plan. a. Due to the abundance of multipath~>signals we changed the flight plan to allow.the F-101 to make repeated rendezvous from a distance of 20-25 miles. b. During these rendezvous a combination of antenna.positions were tried in an effort to eliminate the multipath signals and/or break a false lock the F-101 might have had at any particular time. This had no effect. 4. Interference: a. During the flight considerable interference was noted which caused the AGC and the PRF to increase. This would have a detrimental effect on sensitivity. b. By process of elimination, the interference was isolated to the tankers' IFF and APN-21 TACAa. sic ET Approved For Release 2005/04/21 : CIA-RD071B00399R0003001-60001-9 25X1 Approved For :Release 20.05/04/2$ 99R000300160001-%p 1148. Page 3. Of - 5. Returned to flight plan inbound to homep~ate. a. Departed orbit path as briefed for homeward leg. During this period the F-101 attempted rendezvous from approximately 20 miles astern to a position 5 miles in trail. b. Multipath signals were very prevalent as F-101 attempted to lock on false signal. A false lock was bbtained at 5 miles and was maintained 2 1/2 miles high for 5-6 minutes over varying terrain. c. During this phase all antennas positions were tried and the F-101 was asked to make various maneuvers all to no avail. The false lock was maintained. d. When the false lock was manually broken by changing channels.: the proper lock was re-established. There is no guarantee of this however. E. Post flight 1. Removed units from tanker and F-101. 2. Realig::ed units for next days flight. 30 A. Noveraber 1966 Cor.ditiou of TACAN units prior to flight 1. S/N 805 (tanker): 10DB rejection - instrumented, 2. S~I~ W7 (tanker): 6.5 DB rejection - instrumented 3. ALT350 (F-101): 12 DB rejection B. Test flight 1. Aborted mission - pilots window shattered. 2.- Returned to-tanker's home station with crew 1 December 1966 A: Returned to B.. Condition of TACAN units'irior forflight 1. 'Same.-as..: IV A. C: Test flight .12:15 T.O. 1? 0/1V VV";', tnv[v, i.an .....~ - --- - - +-44-4o' lock on'was obtained by the tanker at 72 les.:: a. F-101 had no lock on up to 57 miles- (during this.period; this phase the IFF was muted to prevent inter- in D b g ur . ference and we changed channels to Ch 98. The F L101,-.1_4-:__` still had no lock on. 2. Changed tanker's TACAP: unit. a. Installed S/N Q127 b. F-10l established lock at 55 miles. Tanker had no loek until 4 miles. SECRET Approved For Release 2005/04/21 : CIA-RDP71B00399R000300160001-9 Approved For Release'2045/ @]IB00399R000300'46dOQ1=9.': Page 4 of 3. Altitude charge due to weather a. After refueling, F-101 descended to 26M followed shortly by the tanker. b. During this descent the maximum separation was approximately 20 miles and a lock was maintained by both aircraft. At this time a -single multipath signal was observed. This signal was strong for approximately 30 seconds and then became weak and intermittent, and disappeared. b. Another signal wac observed momentarily at 7 1/2 miles 4. Distance check with S/N QJZ-27 installed. a. F-101 made a distance run to check sensitivity of 6.5 DB rejection level. b. Tanker broke lock at 7.5 miles c. F-101 maintained lock to 43 miles where he was recalled.' NOTE: Up to this time.all the F-101 TACAN reply pulses were marginal at best.' At this point they became weak and intermittent. No further lock on was obtained by the tanker. d. On the return from the distance run, the F-101 maintained lock all the way in to hook up. Tanker had no lock on whatsoever. - 5. Reinstalled S/N 805 in tanker. but was very weak and intermittent. d. No other problems were observed during this rendezvous. a. F-101 made another 20 mile run with no lock on by..either aircraft. b. Requested F-101 close to .3 miles and maintain' trail the tanker: an effort to re=establish contact. This effort was i' c. During. this period a-variety'of equipment. was'; changed I c. Tried to obtain a suppression pulse from tankers (APX-25 IFF with a jumper cable but to no avail. 90.5 miles. b. Same situation, but-IF.F off-'AGC equals 2.8 V (TACANT a. TACANN on Ch 92 A/G. with IFF on - AGC equals 3.5 V Interference from tanker's:'IFF caused a rise in TBCANA d. The testy- was terminated at?this time. D. Post flight 1. Inspected and repaired TACAN units. a. The malfunctions that were found in the equipment explained the problems we were experiencing. A bad tube (V-2501) was found in the F-101 installation. A bad capacitor (C-2513) was found in S/N 805 installed in the tanker. SEC T Approved For Release 2005/04/21 : CIA-RDP71B00399R000300160001-9 vain as the unit in .thei'F-101 was- not replying.;:' 3 ..., SINN.. QjC-27 'TACAN installed ih . Tanker. C.' a.' F-101 maintained-0-25 miles , distance from tanker; and-.. "bottom antenna. b. The false signals were noted out to approx. 20 miles but were most prevalent from 6 to 9,miles. c. Multipaths signals were noted while using the tanker's top antenna but were very few in number and seem to be no problem inside of 5 - 6 miles. d. F-101 made a distance run of approximately 165 miles with no problems as far as sensitivity of the TACAN is concerned. -T . Page * 5 of VI 2 December.1966 A. Condition of TACAN units prior to flight 1. S/id - 805 (tanker): 12 DB rejection - instrumented 2 SIN - QK-27 (tanker): 8DB rejection - instrumented' S/N - ALT-350 (F-101):12 DB rejection B. Test flight 1. Aborted mission - F-101 engine problems a. Departed in KC-135 for normal refueligg mission. Unfortunately this receiver was not A /A TACAN equipped. After completion, we returned to 25X1 VII 8 December 1966 A. Condition of r='ACAN units prior to test. 1. Same as VI A B. Aircraft involved in test 1. F-101 (56-6291) 2. KC-135 (59-10+9) C. Flight Test 1. Tankers TACAN antennas. a. With antenna select switch in "Top" the antenna actually, in use was located on the bottom, and vice versa. This. was due to the antenna coax being reversed on the antenna relay. This was remedied. . b. Also found an improperly assembled coaxial connector on the antenna coax. This was repaired as best we :miles from the tanker multipath-.signals were noted.while, a. While F-101 was in trail ' at; distances varying fr6m-0-25w, 2. S/N 805 TACAN:inetalled intanker could under the circumstances. Approved For Release 2005/04/21 : CIA-RDP71B00399R000300160001-9 on the tanker's bottom antenna. The false .`signals .were ' noted , out to .'approx. x20;miles bat: were moreAprevelant between. .4 to 9.:miZ?a: Multipath :signals were 'noted 'while. using the ,tanker's `aop" `~ antenna t ut were few in number. and', seems to 'tie. no problem problems-as far as~sensitivity of the TACAN is concerned-: trail. Multipath.signals_ were noted on-,the tanker's 4. Interference from the-tanker's own TA CAN and IFF. - a. Owing to the location of the TACAN antennas on the tanker, interference is of prime importance. b. If both of the tanker's TACANS are utilizing their top or bottom antennas simultaneously the interference is unbearable unless there is at least a 15 channel separation between the ARN-21 and the receiver's i.e. the article, F-101, etc.) TACAN. c. If the two TACANS (i.e. the AIUI-21 and APN-52 on board the tanker) are using opposite antennas (i.e. one system on the top and one system on the bottom) the interference is reduced considerably, but still exists. d. The tanker's IFF system also causes interference to a degree that is definitely noticeable. VIII Conclusions: NOTE: All the conclusions and recommendations mentioned in this report are based on a flight test utilizing a KC-135 tanker and an F-101. There was no way we could switch antenna locations, measure video output, or the effect of local interference on the F-101 d i thi ur ng s Plight test. Therefore we are assuming that-the F-101 will react basically the same to multipath signals as. the KC-135. Also her , V e Jn no guarantee LL=T,, the Cygnuillt th s w reace same as `'an F-101 to multipath signals. ' However, ye.-feel.. A. KC-135 Tankers properly as there" N. no appreciable difference in the top orbottom antennas, 2 The seco d tanker ( 14 0 m xi n 9 ) was is 59- redrelti int -,sung,:. ante nas b in r n e g eversed: and. a bad coaialt ..x connecor. BECO14 NDATI0NS a. That all KC-135's.be carefully inspected for the. conditionand location'of.all'coaxial .cables and connectors pertaining to the ARN-52V. B. Rendezvous 1. Multipath signals are definitely present and can cause erroneous range readouts in either/or both aircra?t . 2. The false signals cannot be avoided by alignment of the TACAN equipment alone if the tanker utilizes its bottom TACAI3 antenna position. 3. These false signals can be avoided at the critical ranges by proper alignment of the equipment and if the tanker utilizes its top antenna position only. NOTE: SEE EXCEPTION UNDER INTERFERENCE Approved For Release,2005/04/21 : CIA-RDP71 B00399R000300160001-9 4. A rendezvous can be made with the tanker using the top ARN-52(v) TACAN antenna only. 5. While the tanker is turning to maintain its orbit, the possibility of breaking TACAN lock is greatly increased. This creates more of a problem at closer ranges than at distant ranges. 6. The situation can exist where one aircraft cannot obtain a lock on and the fault is in the other aircraft's unit. C. Interference 1.. Interference from the tanker's ARN-21 TACAN is so severe that an A/A lock is all.but impossible. This condition exists anytime the tanker 'is. using both TACAN syatems'on their top or bottom antennas ' simultaneously and the.ARN-21' t~ %;L&ruIels or the recelver's F-101, etc.) TACAN.? 2. With proper channel and antenna separation, interference i RECOMENDATION a. That the tanker maintain the TACAN antenna selector switch in the "TOP" position for all A/A TACAN rendezvous. b. That all Article pilots and tanker navigators be informed of the possibility of breaking lock when either or both aircraft are in a turn. c. That all TACAN units be nodified to allow the distance readout on the indicator to reset to 000 miles and then go into "search" the first time a lock is' broken and the aircraft are within 50 miles of each other. d. If there is an A/A discrepancy in either or both air craft, that both aircraft are-.written-up, checked and the results made known to the opposite interested party. is s it apparent .but. is not as harmfuil. It'does 61., th e TACAN at greater distances .. es with the A/A'TACAN-in much the same manner'as`described in (2) above..: Thia~ interference is not apparent'at-the closer ranges but; starts to become a factor at approximately 90 miles.:- 4. If the interference described in items-2-and 3 above were eliminated, the maximur} TACAN A/A distance should be increased. 5. It is foreseeable that an interference problem may arise when all the aircraft (i.e., tanker, article and chase) are A/A equipped unless certain precautions are taken. 6. It is possible that a minor interference problem already exists when numerous A/A equipped aircraft are in the same general area.(e.g., more than one AR scheduled). The procedure at present is to maintain a one (1) channel (i.e., one (1) megahertz) separation between conflicting aircraft. This may hot be adequate to prevent minor inter- ference. SECT Approved. For Release 2005/04/21 : CIA-RDP71 B00399R000300160001-9 C. Interference.-(Continued) 1. It appears"that terrain has, no':bearing on" *the quantity, of multipath.signals' .'Althoughtthefalse signals were more- prevalent at "one.-time than 'another. ,this-'':could net bp correlat'ed with any 'type terrain:" Maybe with additional flights and or' special equipment this could be?accomplished. Tliepresent "Minimuat,fperfbrmerlce,-Check" contained~ , ~ NAVWEps : 6-30 .`ARN-52-.2 to ~12R5-2 ' ARN52-2 revised _ 'Ma n_tne' A/A- mode,wil].i pass a ;bench check 'Y' mentioned tecizriical:!publications contain no"proeethire for aligning ahe range': decoder* module'. to. the "12 db're~ection At.present there`is'no A/A TACAN pre-flight capability at ~fflwm SECRET Approved For Release 2005/04/21 : CIA-RDP71B00399R000300160001-9 RECOMMENDATION That the.tanker maintain. the AN-21 TACAN antenna select switch in the "BOTTOM" position and the function switch in the Rec. position during all A/A TACAN rendezvous. b. That if the ARN-21 TACAN must use the "TOP" antenna position for some reason, a channel separation of at least 15 channels be maintained between the ARN-21 and whatever channel the receiver (i.e., the article, F-101 etc.) has set up. c. That supression pulses be fed to the ARN-52 TACAN from the tankers IFF. d. That all pilots are briefed on the possibilities of interfering with other aircraft once the F-101 is e ui ed with A/A TACAII. This briefing can take place at anytime upon request. e. 1 a a spacing of three (3) channels be maintained (e.g., One article on CH 95, another article on Ch 92, etc) between aircraft during multiple refuelings. Channel 95 should remain the primary A/A refueling channel. E. Maintenance (Continued) RECOMMENDATION; a. That a common "Minimum Performance Standard" which includes a complete A/A check be adopted by maintenance facilities. b. That a common "Module Alignment Procedure" which includes a complete A/A check be adopted by both maintenance facilities.. c. That a pre-flight capability for checking the A/A TACA:N mode be established at the tanker's home station. This would insure the soundness of the installation before take-off. d. The maintenance procedures mentioned in (a) and (b) above are presently being tested at =and will be available upon their validation. e. That three TACAIJ units from the tanker organization be aligned using the new procedure. These units would be used in the same tankers (or I Ishould be kept informed as to what tankers do have tee units installed) so the new maintenance procedux can be. properly evaluated. These units can be aligned IX Summary A. The multipath signals which cause the abnormal TACAI A/A distance readouts are definitely present and will continue to exist:.- However, we feel with proper maintenance, informed crews, adequate hardware, and rendezvous procedures that are.closely adhered to a successful A/A TACAAN rendezvous can be-made without the danger of false information being displayed due tot:multipath This test was conducted using theRT-384/ARN-52(V) TACAN which i's_ capable of displaying range only in the A/A mode'. A modification is.,pending which will allow the.TACATI to provide both rrange.and bearing in the A/A' mode . The modification requirements for the involved aircraft are as follows: 1. The ARN-52(V).TACAII system is to be replaced.by the ARN?.90. TACAN system. This involves structural and wiring changes. 2. The SRN-90 consists of: a. AS-2057 Antenna b. MX-7731 Bearing Data Unit c. CU-1688 Directional Coupler d. MT-3834'Shock Mount, Base e. ET-863 Receiver- Transmitter 3. Delivery Schedule of RT-863 P .-T a. 15 Jan 1967 5 units 15 Mar 1967 5 units 15 May 1967 10 units 15 Jul 1967 10 units B. A-12 1. No additional aircraft wiring is required T 25X1 25X1 Approved For Release, 2005/04/21 : CIA-RDP71 B00399R000300160001-9 B. A-12 (Continued) 2. The AT-384/ARbi-52V is to be modified by a kit consisting of a new module and a printed circuit'board. 3. After!this,modification is complied with the unit will be designated Rr-864/AN -52(V). 4. Delivery schedule of modification kits. a. 10 Jan 2 kits d. 15 Mar 5 kits b. 31 Jan 2 kits e.. 15 Apr 10 kits c. 15 Feb 2 kits f. 15 May 9 kits C. F-101 1. Replace the existing ARN-21 TAAAN with the RT-384/AFIt-52(V) a. This naturally involves rewiring the F-101 2. The P -384/A N-52(V) is to be modified by a kit consisting of a new module and a printed circuit board. 3. Delivery schedule for the RT-384/AF.IN-52(V) a. Start of delivery is 1 April 1967 to, be completed by 30 April 1967. 4. Delivery schedule of modification kits a. Same as 34 above (A-12 will get first kits) SECRET Approved For Release 2005/04/21 : CIA-RDP71B00399R000300160001-9