Monthly Millions Of Service Hours
1921-07-01 294.700
1921-08-01 321.700
1921-09-01 313.400
1921-10-01 334.700
1921-11-01 313.500
1921-12-01 297.800
1922-01-01 279.000
1922-02-01 258.700
1922-03-01 301.200
1922-04-01 282.000
1922-05-01 305.800
1922-06-01 315.000
1922-07-01 270.600
1922-08-01 313.200
1922-09-01 321.000
1922-10-01 351.800
1922-11-01 340.900
1922-12-01 335.100
1923-01-01 343.800
1923-02-01 307.600
1923-03-01 358.400
1923-04-01 344.200
1923-05-01 366.900
1923-06-01 366.400
1923-07-01 365.900
1923-08-01 383.700
1923-09-01 350.700
1923-10-01 382.300
1923-11-01 345.900
1923-12-01 322.700
1924-01-01 330.000
1924-02-01 310.000
1924-03-01 334.200
1924-04-01 332.500
1924-05-01 337.300
1924-06-01 318.800
1924-07-01 330.000
1924-08-01 333.100
1924-09-01 331.000
1924-10-01 358.100
1924-11-01 319.700
1924-12-01 325.300
1925-01-01 327.500
1925-02-01 295.100
1925-03-01 326.900
1925-04-01 325.300
1925-05-01 327.200
1925-06-01 333.600
1925-07-01 339.800
1925-08-01 339.200
1925-09-01 331.500
1925-10-01 353.900
1925-11-01 322.200
1925-12-01 328.900
1926-01-01 318.600
1926-02-01 296.100
1926-03-01 340.300
1926-04-01 333.500
1926-05-01 336.700
1926-06-01 344.400
1926-07-01 350.000
1926-08-01 351.700
1926-09-01 341.300
1926-10-01 355.800
1926-11-01 336.400
1926-12-01 334.000
1927-01-01 319.300
1927-02-01 291.800
1927-03-01 336.300
1927-04-01 328.100
1927-05-01 334.000
1927-06-01 341.700
1927-07-01 333.200
1927-08-01 346.600
1927-09-01 326.900
1927-10-01 338.600
1927-11-01 313.600
1927-12-01 305.100
1928-01-01 296.200
1928-02-01 281.800
1928-03-01 312.700
1928-04-01 301.200
1928-05-01 324.200
1928-06-01 321.700
1928-07-01 316.900
1928-08-01 333.400
1928-09-01 307.300
1928-10-01 337.900
1928-11-01 306.300
1928-12-01 292.100
1929-01-01 300.400
1929-02-01 272.900
1929-03-01 308.000
1929-04-01 313.100
1929-05-01 326.500
1929-06-01 317.600
1929-07-01 330.800
1929-08-01 339.200
1929-09-01 313.100
1929-10-01 341.200
1929-11-01 303.600
1929-12-01 288.800
1930-01-01 289.800
1930-02-01 259.100
1930-03-01 286.300
1930-04-01 288.900
1930-05-01 294.600
1930-06-01 276.400
1930-07-01 275.500
1930-08-01 271.200
1930-09-01 258.600
1930-10-01 268.600
1930-11-01 233.300
1930-12-01 235.800
1931-01-01 232.900
1931-02-01 207.700
1931-03-01 231.900
1931-04-01 232.100
1931-05-01 230.300
1931-06-01 227.700
1931-07-01 226.900
1931-08-01 218.900
1931-09-01 207.300
1931-10-01 211.000
1931-11-01 183.600
1931-12-01 184.400
1932-01-01 176.800
1932-02-01 169.900
1932-03-01 186.400
1932-04-01 176.700
1932-05-01 174.500
1932-06-01 168.400
1932-07-01 158.100
1932-08-01 161.300
1932-09-01 156.300
1932-10-01 166.300
1932-11-01 157.200
1932-12-01 155.700
1933-01-01 148.100
1933-02-01 134.600
1933-03-01 146.400
1933-04-01 140.600
1933-05-01 152.000
1933-06-01 155.000
1933-07-01 160.800
1933-08-01 173.400
1933-09-01 166.400
1933-10-01 172.700
1933-11-01 158.400
1933-12-01 153.100
1934-01-01 159.800
1934-02-01 147.300
1934-03-01 171.700
1934-04-01 165.400
1934-05-01 178.000
1934-06-01 177.200
1934-07-01 173.600
1934-08-01 177.700
1934-09-01 162.700
1934-10-01 176.300
1934-11-01 158.100
1934-12-01 155.900
1935-01-01 164.500
1935-02-01 149.100
1935-03-01 165.500
1935-04-01 163.200
1935-05-01 169.800
1935-06-01 166.200
1935-07-01 172.100
1935-08-01 174.200
1935-09-01 163.500
1935-10-01 181.300
1935-11-01 164.500
1935-12-01 164.700
1936-01-01 173.100
1936-02-01 172.500
1936-03-01 180.800
1936-04-01 182.900
1936-05-01 184.000
1936-06-01 187.900
1936-07-01 193.300
1936-08-01 192.200
1936-09-01 191.400
1936-10-01 204.600
1936-11-01 185.300
1936-12-01 194.100
1937-01-01 187.300
1937-02-01 178.100
1937-03-01 205.000
1937-04-01 202.400
1937-05-01 204.600
1937-06-01 210.100
1937-07-01 211.100
1937-08-01 207.700
1937-09-01 196.800
1937-10-01 199.300
1937-11-01 179.500
1937-12-01 173.800
1938-01-01 162.100
1938-02-01 146.100
1938-03-01 165.100
1938-04-01 154.400
1938-05-01 153.200
1938-06-01 157.200
1938-07-01 157.800
1938-08-01 169.100
1938-09-01 165.500
1938-10-01 174.600
1938-11-01 164.800
1938-12-01 165.900
1939-01-01 162.400
1939-02-01 150.300
1939-03-01 173.400
1939-04-01 161.000
1939-05-01 171.300
1939-06-01 176.400
1939-07-01 173.800
1939-08-01 184.000
1939-09-01 179.000
1939-10-01 194.800
1939-11-01 182.500
1939-12-01 175.300
1940-01-01 179.400
1940-02-01 165.200
1940-03-01 175.300
1940-04-01 174.600
1940-05-01 182.200
1940-06-01 179.900
1940-07-01 190.600
1940-08-01 196.200
1940-09-01 184.100
1940-10-01 201.700
1940-11-01 182.800
1940-12-01 182.400
1941-01-01 187.000
1941-02-01 170.800
1941-03-01 194.600
1941-04-01 196.800
1941-05-01 210.700
1941-06-01 211.500
1941-07-01 223.900
1941-08-01 227.000
1941-09-01 221.600
1941-10-01 236.600
1941-11-01 213.300
1941-12-01 222.100
1942-01-01 220.400
1942-02-01 198.900
1942-03-01 226.500
1942-04-01 231.200
1942-05-01 235.000
1942-06-01 240.800
1942-07-01 246.600
1942-08-01 251.100
1942-09-01 243.800
1942-10-01 259.400
1942-11-01 238.900
1942-12-01 251.700
1943-01-01 246.600
1943-02-01 228.400
1943-03-01 261.000
1943-04-01 253.600
1943-05-01 252.600
1943-06-01 258.400
1943-07-01 261.700
1943-08-01 263.600