AC 20-52

Appendix 6 AC 20-52 Page 2 8/24/67

(8) A one-inch crack in the lower skin of the right wing was found during a periodic inspection. The crack was located at W.S. 185 and 16 inches behind the center spar. Total flight time on the aircraft was 45,987 flight hours. A repair can be found in the

(9) A one-inch chordwise crack was found in the upper inboard attach 19) A get her one aret. angle of number one nacelle where it is attached to the front tang of the center spar. Also, a one-inch crack was found in this same angle where it attaches to the aft tang of the center spar. Approved repairs were accomplished. The aircraft total time was 23,749 flight hours.

« the cente pet tape the cet fa. (10) During a block overhaul, the upper left wing skin was found to be cracked at station 130. The crack was located forward of the center spar tangs. The crack ran diagonally and was two inches long. No other discrepancies were noted in the surrounding structure.

(11) Two chordwise cracks were found in the right wing lower skin at the stringer and fittings located at station 281. Manufacturer has a service bulletin covering the repair in this area. The total time on the aircraft was 18,214 flight hours.

(12) A two-inch crack was detected during a visual inspection in the box beam. The crack was located in the lower side of the right center forward and of the box beam in the aft cargo compartment.

The repair for this area can be found in the manufacturer's structural repair manual. The total time on the aircraft was 47,045 flight hours.

(13) A crack was found in the inboard attach angle at the center spar bolt in No. 4 engine nacelle. This was repaired in accordance with the manufacturer's repair manual.

(14) During a visual and dye penetrant inspection, a one-half inch crack was found in the gyro-support bracket. The crack extended from the bracket hole to the edge of the spar at the forward tang of the lower front spar cap at station 4. A repair was made in accordance with the manufacturer's structural repair manual. The total time on the aircraft was 44,155 flight hours.

(15) Stringer No. 18, located at station 300, was found to be cracked. The repair was made in accordance with manufacturer's Service Bulletin No. 561. The total time on the aircraft was 23,725 flight hours.

AC 20-52 Appendix 6 8/24/67 Page 3

(16) A three-inch crack was found in the attach angle at the point where the wing is joined to the fuselage aft of the front spar. The repair was accomplished in accordance with an approved repair. The total time on the aircraft was 23,725 flight hours.

(17) During a basic service inspection, the bottom tang of the left wing front spar was found cracked at station 160.

The repair was accomplished in accordance with the manufacturer's service bulletin.

(18) A crack was found in the wing attach angle doubler where the wing joins the fuselage at station 400. A repair can be found for this area in the manufacturer's repair manual.

(19) During overhaul, spanwise stringer No. 23 on the lower то торті но тоно wing surface was found cracked. The crack ran chordwise in the stringer crown and was located at W. S. 325.

The repair was accomplished in accordance with an approved repair method. Total time on the aircraft was 18,164 flight hours.

(20) The right wing lower skin was found to be cracked between the front and rear spars at W.S. 281. This repair was made in accordance with an approved repair method. Total time on the aircraft was 23,725 flight hours.

(21) Cracks were found in the left wing fuel tank access plate doublers 182b and 182c. Manufacturer's Service Bulletin No. 799 covers the repair of this area. Total time on the aircraft was 23,752 flight hours.

(22) During overhaul, the right-hand splice angle, P/N 42435221, on the nosewheel beam forward pressure bulkhead was broken.

The attach angle was replaced with a new part. Total time on aircraft was 51,368 flight hours.

(23) The right center spar tang was found cracked at the bolthole outboard of the fuselage skin. Also, the attach angle was cracked at the same bolthole. This crack was approximately one inch in length. Manufacturer's Service Bulletin No. 678 covers the repair of this area. Total time on the aircraft was 48,958 flight hours.

(24, A four-inch crack was detected, by visual inspection, in the radius of the bottom vertical angle of the front spar at station "O". The angle was replaced. Also, a two-inch crack was found in the front spar on the left side of the conduit hole located at station 28. A doubler was installed.

Total time on the aircraft was 47,112 flight hours.

Appendix 6 AC 20-52 Page 4 8/24/67

(25) A visual inspection revealed that the upper wing skin was heavily corroded in the area just forward of the rear spar at station 167. The section of wing skin was replaced.

Total time on the aircraft was 45,73? flight hours.

During inspection, corrosion was noted on the doubler of the left wing trailing edge between stations 300 and 357.

A section of wing skin was removed that was 37 1/2 inches long and 10 3/4 inches wide. A repair for this area can be found in the manufacturer's repair manual.

(27) Inspection of the center lower spar cap revealed a crack that progressed fore and aft through the cap and upwards into the spar web approximately three inches. The crack was located in the left wing at W.S. 170 under the No. 2 outboard lower fairing. Aircraft total time was 37,386 flight hours.

(28) During aircraft overhaul, the right main loading gear drag strut to the front spar fitting, P/N 5325648, was found cracked. The crack was located in the inboard brushing bore adjacent to the bore for the large trunnion nut.

Aircraft total time was 52,263 flight hours.

b. Fuselage.

(1) Inspection of the fuselage during a block overhaul revealed that the skin was cracked at the emergency exit cutout on the right side of the fuselage at station 557. The operator established an inspection of this area in its maintenance program to preclude further cracks. The total time on the

(2) During a block overhaul, the left ice plate was removed from F.S. 260. A one and one-half inch crack was found that was progressing vertically between stringers Nos. 21 and 22.

Also, a one-inch crack was progressing horizontally between stringers Nos. 22 and 23. The total time on the aircraft was 23,749 flight hours.

(3) During a service inspection, cracks were found in the frame to foot fittings doubler at stations 497.5 and 498.5.

The repairs were accomplished in accordance with the manufacturer's recommendations.

(4) The fuselage circumferential flange to the left stringer No. 24 was found cracked at station 238L. The affected part of the flange was replaced.

AC 20-52 Appendix 6 8/24/67 Page 5

(5) Corrosion was found around cabin windows 2, 3, 5, 7, 8, 9, and 10 on the left side of the fuselage and 4, 7, and 10 on the right side. The areas were cleaned, treated, and the metal replaced as required.

(6) During overhaul, the upper fuselage attach angle was found cracked. Repairs were accomplished in accordance with the manufacturer's manual.

(7) During an airworthiness directive compliance inspection, a transverse crack was found in the frame at F.S. 95.

The crack was located just above longeron No. 10. Repairs were made in accordance with the manufacturer's instructions.

Aircraft total time was 27,341 flight hours.

(8) During overhaul, the wing skin to fuselage from attachment channel, P/N 5503731-1 and -2, was found cracked.

The crack is located at F.S. 413 on the left side and it progressed through the upper inboard horizontal flange and vertical leg of the channel. The channels were replaced. Aircraft total time was 30,143 flight hours.

c. Stabilizers During a periodic inspection, a fitting, P/N 4801674, was found cracked. The fitting is located on the right stabilizer at station 60. The combined length of the ст нав прес ва five short cracks was 6 1/8 inches. The fitting was replaced and continued inspection of this area is planned. The total time on the aircraft was 37,287 flight hours.

(2) During a periodic inspection, the right horizontal stabilizer attach fitting, P/N 4361674-1, was found to be cracked. This fitting is located at station 63 forward and on the top of the front spar. The fitting was replaced and inspection of this area will be continued at the periodic inspection period. The total time on the aircraft was 45,759 flight hours.

(3) The left horizontal stabilizer spar lower forward outboard fitting was found cracked. The fitting was replaced. Total time on the aircraft was 46,369 flight hours.

(4) During a service inspection, corrosion was found on the aft leg of the rear spar attach fitting, P/N 5361821, at the vertical stabilizer stub. The fitting was replaced.

Aircraft total time was 35, 071 flight hours.

Appendix 6 AC 20-52 Page 6 8/24/67

d. Flight Controls.

(1) A ten-inch tear was found in the right-hand wing flap during a service check. This tear was located at station 415 and the tear was from inside out. The fairing at this station also had 10 rivets pulled loose. A repair was made in accordance with the operator's structural manual. Total time on the aircraft was 46,597 flight hours.

(2) A visual inspection revealed a cracked flap support, P/N 5329659. This was a complete failure of the part. The location of the part is at the right W.S. 167. The flap support assembly was replaced. The total time on the aircraft was 47,418 flight hours.

(3) The right-hand flap hinge was found cracked at the forward outboard corner of the hinge fitting station 281 at the flap link cutout P/N FLA 1055. The flap assembly was replaced.

(4) When the flaps were extended beyond 30 degrees, the aircraft would make a turn to the left. Inspection revealed that the outboard flap linkage, P/N 5534780, was broken on the left wing flap. Time since overhaul was 1,959 flight hours.

DC-7 AIRCRAFT MAINTENANCE INFORMATION. The following is a listing of significant maintenance difficulties that have been reported by air carriers as mechanical reliability reports from 1964 to 1967. This information may be useful in identifying additional structural inspection areas:

2. Wings.

(1) Corrosion was found on the inner strut of the nose landing gear where it attaches to the fork. This was repaired by replacing the inner strut. Aircraft total time was 24,588 flight hours.

(2) During inspection, a two and one-half inch crack was found in frame P/N 5361581 at W.S. 50 between longeron 9 and 10 due to fatigue. Repairs were made in accordance with the manufacturer's instructions. Aircraft total time was 44,879 flight hours.

(3) A one and one-half inch crack was found in the upper wing skin during a routine inspection. The crack was located approximately two inches inboard of the No. 2 main fuel tank filler cap. Repairs were made in accordance with the manufacturer's instructions.

AC 20-52 Appendix 6 8/24/67 Page 7

(4) During wing flap retraction, bolt P/N 2356375 failed in the link assembly P/N 4325008 at W.S. 378. The outboard flap shifted outboard riding on top of the right aileron holding it in the down position. The link assembly and flap were replaced. Aircraft total time was 20,030 flight hours.

(5) During a routine service inspection, a one-inch crack was found in the wing to fuselage attach angle at station 381 on the right wing. Approved repairs were accomplished.

Total flight time on the aircraft was 22,621 flight hours.

(6) The left outboard nacelle circumferential at station 400 was found cracked during aircraft overhaul. The crack was located at stringer No. 8 inside of the nacelle. A repair can be found in the manufacturer's repair manual.

(7) The attach angle on the outboard side of number one nacelle found cracked at the leading edge of the wing. Also, the inboard top attach angle was cracked at the bolts on both sides of the center spar. Approved repairs were accomplished.

(8) During overhaul, a crack was found on the outboard side of the No. 2 nacelle. This crack was located in the nacelle circumferential at station 384 in the "j" box area. Approved repairs were made in accordance with the manufacturer's repair manual.

(9) During overhaul, the Nos. 2 and 3 main tuel tank doublers were found cracked at station 203. The manufacturers have a service bulletin covering the repair in this area.

(10) The fuselage attach angle doublers on top of the left and right wings were found cracked during aircraft overhaul. The cracks were located at W.S. 40. This was repaired by replacing the attach angle doublers.

During a routine heavy service inspection, the wing to fuselage attach doubler was found cracked aft of the top forward spar attach fitting. The doubler was replaced. Also, No. 3 top outboard nacelle attach angle was found cracked in the angle radius. The crack was located approximately 12 inches forward of the front spar. A repair was made in accordance with the manufacturer's structural repair manual.

The total time on the aircraft was 20,143 flight hours.

(12) Inspection during a heavy service basic check period revealed that the nacelle to wing inboard attach angles in the Nos. 1 and 2 positions were cracked. The No. 1 attach angle contained a one and three-eighths of an inch chordwise crack slightly above the angle bend radius. The No. 2 attach

Appendix 6 AC 20-52 Page 8 8/24/67 angle was cracked between the rivets adjacent to the bend radius in a chordwise direction approximately one inch forward of the front spar. Also, it had a one and one-half of an inch crack in the aft end of the angle in the center of the bend radius directly over the rear spar. Both cracks were repaired in accordance with approved manufacturer's drawings. The total time on the aircraft was 19,345 flight hours.

Inspection revealed a three-sixteenth of an inch crack in the right top wing skin at the outboard aft corner of No. 3 alternate tank accessory plate cutout. Also the plate landing was cracked. The repair was accomplished by installing an outside doubler - 90-7075-56, on the skin crack and the accessory door landing was spliced. The total time on the aircraft was 15,597 flight hours.

(14) During a block overhaul, inspection revealed that the left wing skin was cracked from the center spar aft of the access cutout at W.S. 203. The repair was made in accordance with the manufacturer's drawings. A special X-ray inspection of station 203 on the right and left wings of the fleet was conducted. The total time on the aircraft was 29,850 flight

(15) During a special inspection, the following damage was found on the left wing: The upper wing skin was cracked at 16 places at station 167 between the front and center spars. The length of these cracks ranged from one-fourth of an inch to five inches long. Also, the upper wing skin was cracked threefourths of an inch at station 141 between wing stringers Nos.

6 and 7. In addition, the lower skin was cracked at station

167. This crack was six inches long and was progressing forwardfrom the rear spar. Repairs were accomplished in accordance with the manufacturer's recommendations.

(16) Special inspection of the wings disclosed the following damage:

The right upper wing skin was cracked in seven places between the front and center spars at station 167. The length of the cracks ranged from one-eighth of an inch to three and threeeighths inches long. The left upper wing skin was cracked in 16 places between the front and rear spars at station 167. The length of the cracks ranged from one-fourth of an inch to five and three-eighths inches long. The left upper wing skin was cracked at station 133 aft of the center spar. This crack was three-fourths of an inch long. Cracks three-fourths of an inch long were also found in the upper wing skin at station 152 just aft of the center spar. In addition, seven cracks were found just aft of the center spar from station 132 to station 152.

These cracks were one-eighth to four and seven-eighths inches The repairs were made in accordance with the manufacturer's recommendations.

AC 20-52 Appendix 6 8/24/67 Page 9

b. Stabilizers.

A nine-inch crack was detected during a routine inspection in the lower surface of the left stabilizer at station 107.

The aft end of the crack was located 12 inches from the rear edge of the stabilizer and its direction of progression was fore and aft through the row of rivets attaching the skin to the rib. The internal structure of the stabilizer was not affected. The repair was made in accordance with the structural repair manual.

c. Hydraulic Systems.

Hydraulic fluid was lost when the flaps were extended during descent. Also, when the landing gear was extended, the pressure dropped to 900 p.s.i. Investigation of the aircraft after landing disclosed that the manual bypass valve was cracked at the fluid port. The valve was replaced.

(2) Hydraulic fluid and pressure were lost during taxiing resulting in the use of the airbrakes. Inspection revealed that the inboard flap actuator on the left wing was leaking.

(3) After takeoff, all hydraulic pressure and fluid were lost.

Inspection revealed that the manual bypass valve, P/N 3408466-1, had failed. The piston, P/N 2243941, failed at the lever attach end at the necked-down section in the 11/32-inch diameter area. The valve was replaced and the

(4) During taxi after completion of the landing roll, all hydraulic pressure and fluid were lost. Inspection revealed that the right inboard flap cylinder, P/N 3498899-1, was cracked. The flap cylinder was replaced and operation of the system was normal.

d. Landing Gear System.

The landing gear was lowered for landing and the nose gear would not come down. However, after several attempts, it did come down and lock. The aircraft was jacked and on the retraction test, the gear would not move. Upon removal of the control valve, P/N 3480940-1, the "up" port was found to be blocked. Disassembly of the valve revealed that the port was blocked by soft solder. As a result of these findings, the hydraulic manifold was replaced and the system flushed.

Appendix 6 AC 20-52 Page 10 8/24/67

e. Flight Controls.

(1) During routine inspection, the right wing flap supports at station 281 and the right and left supports at station 372, P/N 5498283-2 and 5498340 were found to be corroded beyond specified limitations. Corrosion of the supports is considered to have resulted from the aircraft being in storage for seven months. The total time on the aircrait was 20,143 flight hours.

(2) During overhaul, zyglo inspection of the elevator torque tube revealed that the right end attach fitting, P/N 3536439-3, was cracked. The crack was three-eighths of an inch long and extended from outboard through the bolthole. The defective part was replaced.

(3) During a maintenance operation, a flap link assembly, P/N 549334, was found broken at the outboard end of the left flap. The failure occurred in the link-bearing area.

The total time on the aircraft was 22,249 flight hours.

Fuselage.

(1) The following discrepancies were noted during a routine inspection: The left side of the fuselage skin was cracked in the rivets below the pilot's sliding window at station

41. The length of the cracks ranged from one-half to three-quarters of an inch. Eight cracks that ranged from a half to one and one-half inches in length were found in the skin below the pilot's window at station 22 between stringers Nos. 15 and 22. The fuselage skin was also cracked on the left side at stringer No. 15 and F.S. 58.

The length of these cracks was one and one-half inches in length. In addition, cracks one and one-half inches in length, were found on the right side of the fuselage at stations 21 and 22. Repairs to these cracks were made in accordance with the manufacturer's structural repair manual. The total time on the aircraft was 22,621 flight hours.

(2) During a basic check period, the fuselage skin was found to have cracked beyond the stop drill hole at the left forward emergency exit upper hinge. Repairs were accomplished in accordance with the manufacturer's structural repair manual.

The total time on the aircraft was 20,143 flight hours.

AC 20-52 Appendix 6 8/24/67 Page 11

(3) A two and one-half-inch crack was found in the nose gear well web on the left side at station 58. The repair was accomplished in accordance with the manufacturer's structural repair manual. The total time on the aircraft was 19,904 flight hours.

(4! During the accomplishment of DSB 275, the fuselage former at F.S. 49.6 was found cracked. The crack was located between fuselage stringers Nos. 8 and 9 above the crew entry door. Aircraft total time was 28,225 flight hours.

AC 20-52 CHG1 Appendix 7 7 Jul 72 Page 1

1. DC-6/-7 STRUCTURAL INSPECTION ITEMS.

a. Emergency Exit Door Hinges.

(1) Location. Fuselage emergency exits (see Figure G-3, Appendix 7).

(2) Applies to DC-6/7 series aircraft.

(a) Action. All aircraft with emergency exit door hinges with less than a one-inch (1") door skin recess radius should have the hinges replaced. Applies to all models DC-6 series prior to serial number 44888 and DC-7 series up to serial number 44872 having 32,000 or more hours time in service.

(3) Other Reference Documents.

(a) DC-6 Service Bulletin 848.

(b) DC-7 Service Bulletin 393.

(4) Probable Consequences. Failure of one hinge can cause failure of the second hinge resulting in loss of the emergency exit door •

(5) Recommendations. Periodic inspection of hinges having 1-inch door skin recess radius to assure continued structural integrity.

b . Emergency Exit Door Hinge Cutouts.

(1) Location. Fuselage Emergency Exits (see Figure G-4, Appendix 7).

(2) Applies to DC-6/7 series aircraft.

(3) Other Refcrence Documents.

(a) DC-6/-7 Advisory Circular 20-52 Appendix 4, Page 10.

(b) DC-6 Service Bulletin 623.

(c) DC-7 Service Bulletin 79.

(4) Probable Consequences. Extension of fuselage cracks initiating at hinge radius could result in more extensive structural damage.

(5) Recommendations.

(a) Periodic inspections until the preventive rework of Service Bulletin 623 or 79 is incorporated.

(b) Perform subsequent periodic inspections commencing at a later date to insure continued structural integrity after incorporation of Service Bulletin 623 or 79 preventive rework.