MAINTENANCE MINUTE ALL TORQUED UP
By Scott Skola
Ever get all torqued up reading a helicopter
maintenance manual
because you couldn’t remember the difference between a re-torque and a torque check? I did, until I had their definitions tattooed on my — well, that’s another story.
In the meantime, let’s work out their definitions here. Because not understanding the difference between a “re-torque” and a “torque check” can lead to potentially disastrous consequences.
When a re-torque is specified by a maintenance procedure, it requires backing off the identified fastener one to two turns, then re-torquing the fastener to a required torque value or predetermined index point.
For example, on an Airbus AS350 there is a 30-hour re-torque requirement for the tailboom mount hardware after installation. It requires indexing the tailboom attachment nut to the tailboom ring with a marker, loosening the nuts (one at a time),
re-torquing the nut to the required value, recording that torque value, and finally checking that the index mark lines up between the nut and the ring.
On the other hand, when a torque check is specified, the fastener is left in place while torque is applied in the tightening direction until the required torque value is reached. If the fastener moves before the minimum torque value is reached, a second torque check will be required at a future time.
For example, on a Bell 206 there is a 1-hour to 5-hour torque check on the main rotor mast nut after each main rotor hub and blade installation. It requires removing the mast nut lock and torquing the mast nut (in the tightening direction) to a specified torque value. If the nut moves (i.e., tightens farther) the mast nut lock is reinstalled and another torque check is entered in the aircraft logbook due at the next 1 to 5 flight hours.
Imagine if a mechanic mistakenly performs a re-torque instead of a torque check on an
item that may inadvertently shift position when the original torque is released. While the Bell 206 is not as susceptible, loosening the mast nut prior to applying tightening torque could cause the main rotor hub to shift on the mast split cones.
However, in the case of a Bell 407, especially with the older lower cone sets, loosening the mast nut would invariably cause a hub shift, leading to another round of main rotor track and balance procedures.
And there can be similar problems with performing a torque check in place of a re-torque. Some installations may require the installed part to shift or resettle. For example, most wheel bearings have an initial torque that is followed by a lower re- torque. Or, aircraft fuel tank mount straps may bind after the initial installation and should be loosened to relieve any binding prior to the strap re-torque.
So, there you have it. As long as you don’t cross your “re-“ with your “check,” life should remain grand. Tattoos optional.
About the author: After 32 years maintaining helicopters in various capacities, Skola concluded a full-time career with a major operator in 2014. When not pursuing future writing projects, he can still be seen around the flight line tinkering on aircraft for beer money. He can be contacted at
tekaviationllc@gmail.com.
22 May/June 2019
Page 1 |
Page 2 |
Page 3 |
Page 4 |
Page 5 |
Page 6 |
Page 7 |
Page 8 |
Page 9 |
Page 10 |
Page 11 |
Page 12 |
Page 13 |
Page 14 |
Page 15 |
Page 16 |
Page 17 |
Page 18 |
Page 19 |
Page 20 |
Page 21 |
Page 22 |
Page 23 |
Page 24 |
Page 25 |
Page 26 |
Page 27 |
Page 28 |
Page 29 |
Page 30 |
Page 31 |
Page 32 |
Page 33 |
Page 34 |
Page 35 |
Page 36 |
Page 37 |
Page 38 |
Page 39 |
Page 40 |
Page 41 |
Page 42 |
Page 43 |
Page 44 |
Page 45 |
Page 46 |
Page 47 |
Page 48 |
Page 49 |
Page 50 |
Page 51 |
Page 52 |
Page 53 |
Page 54 |
Page 55 |
Page 56 |
Page 57 |
Page 58 |
Page 59 |
Page 60 |
Page 61 |
Page 62 |
Page 63 |
Page 64 |
Page 65 |
Page 66 |
Page 67 |
Page 68 |
Page 69 |
Page 70 |
Page 71 |
Page 72 |
Page 73 |
Page 74 |
Page 75 |
Page 76 |
Page 77 |
Page 78 |
Page 79 |
Page 80 |
Page 81 |
Page 82 |
Page 83 |
Page 84 |
Page 85 |
Page 86 |
Page 87 |
Page 88
