SAE AS4059: The American standard for fuel cleanliness
SAE AS4059 is the standard that regulates fuel cleanliness in the US and Canada. It is the latest revision of the now defunct NAS 1638 code, which was developed in 1964 to define classes of particulate contamination in aircraft components and hydraulic fluids, but has been invalid since 2001 and has since been replaced by SAE AS4059.
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The SAE AS4059 standard is a code set by the Society of Automotive Engineers (SAE International) to measure the solid particulate content of fuel samples and hydraulic fluid.
SAE International is a U.S.-based, globally active professional association and standards developing organisation for engineering professionals in various industries.
The below table shows how solid particulate contamination in fuel can be classified according to the SAE AS4059 code. The figures refer to the solid particle count per millilitre of stored fuel.
| Maximum contamination limits (particles per ml) | ||||||
| Size code | A | B | C | D | E | F |
| 000 | 195 | 76 | 14 | 3 | 1 | 0 |
| 00 | 390 | 152 | 27 | 5 | 1 | 0 |
| 0 | 780 | 304 | 54 | 10 | 2 | 0 |
| 1 | 1,560 | 609 | 109 | 20 | 4 | 1 |
| 2 | 3,120 | 1,220 | 217 | 39 | 7 | 1 |
| 3 | 6,250 | 2,430 | 432 | 76 | 13 | 2 |
| 4* | 12,500 | 4,860 | 864 | 152 | 26 | 4 |
| 5 | 25,000 | 9,730 | 1,730 | 306 | 53 | 8 |
| 6 | 50,000 | 19,500 | 3,460 | 612 | 106 | 18 |
| 7 | 100,000 | 38,900 | 6,920 | 1,220 | 212 | 32 |
| 8 | 200,000 | 77,900 | 13,900 | 2,450 | 424 | 64 |
| 9 | 400,000 | 156,000 | 27,700 | 4,900 | 848 | 128 |
| 10 | 800,000 | 311,000 | 55,400 | 9,800 | 1,700 | 256 |
| 11 | 160,000 | 623,000 | 111,000 | 19,600 | 3,390 | 512 |
| 12 | 320,000 | 1,250,000 | 222,000 | 39,200 | 6,780 | 1,024 |
*This is the exact equivalent to the ISO code 18/16/13, which is the particulate cleanliness level required in Europe for fuel to be recognised as ‘clean’.