Ramon Lopez/WASHINGTON DC
Thousands of airliners powered by Pratt & Whitney JT8D turbofans could be taken out of service temporarily if the US Federal Aviation Administration decides to adopt an engine inspection recommendation published by the US National Transportation Safety Board (NTSB). The move would affect Boeing 727s, 737-100s and -200s, and McDonnell Douglas DC-9s.
In the incident, which was uncontained, the low-pressure turbine in the No. 2 JT8D-17A of a Royal Airlines 727-200 failed during a rejected take-off roll in 1998.
According to the NTSB, an estimated 10,000 JT8D-1 through -17AR engines need strip-down inspections and anti-galling treatment for the LP compressor (LPC) tie-rods whose failure precipitated the turbine breakup. The NTSB said the lack of the anti-galling coating on all 12 of the rods in the inspected engine "-suggests that the problem may be widespread".
The four stages of the JT8D engine's LPC are held together by the tie-rods, which are long bolts. Accident inspection of the Canadian aircraft revealed that one LPC rear tie-rod was corroded and fractured, creating overstress fracturing the other 11 tie-rods, which transmitted stress rearwards to the turbine. Investigators said the initial fracture was caused by galling (surface damage caused by friction). A P&W service bulletin had recommended an anti-galling coating, but the FAA did not make it compulsory.
The Safety Board says the FAA should require that all the designated JT8Ds be disassembled for inspection at the next "shop visit", tie-rods should get anti-galling treatment and the engines should be subjected to repetitive bore- scope inspections.
According to the FAA hazard ranking system, the powerplant fault has the potential to produce "severe" or "serious" consequences which require action.
P&W says the work would only cost an estimated $1,000 per engine should it take place during a scheduled overhaul shop visit, so a great deal hangs on the definition of "shop visit" and the length of time allowed before compulsory inspection. The engine maker says there may be an inspection technique that would alleviate the concerns of the NTSB.
Source: Flight International
