Seeing the Southwest 737 in the mud at Orlando International Airport with a broken nose landing gear this past week reminded me why I think mechanics should think twice about taxiing aircraft for maintenance. Let me say, that I have no idea why the 737 ended up in the mud on its way to a maintenance hangar – could have been anything from bad hydraulics to bad taxiing – but we’re likely to never know because the NTSB has refused to investigate. According to news reports, the NTSB declined to investigate considering the incident a maintenance-related issue that did not have safety of flight implications. I disagree with the NTSB’s decision not to investigate at all. How does it know there were no safety of flight issues if it doesn’t even do an on-sight assessment of what happened?
Maybe the FAA will investigate but it’s unlikely that any finding will be made public. And if only the company does the investigation, we know it won’t be made public. Which is unfortunate for the maintenance community because these investigation reports help us learn what happened so we can prevent similar incidents in the future.
Nonetheless, the incident reminded me why I think it’s generally a better idea to tow aircraft for maintenance than to have mechanics taxi them. Taxiing aircraft – especially modern airplanes with high bypass engines – requires considerably more skill and practice than was necessary in the past. These airplanes, with low fuel, no passengers and no cargo, can move quite fast even with the throttles set at idle power. This requires a constant application of the brakes to keep the aircraft taxiing slowly enough to meet standards which are generally stated as equivalent to a fast walk.
Maintaining such a relatively slow pace is tough with the usual airport pressure to keep things moving and even the occasional urging from air traffic control to expedite clearing the area. Mechanics taxiing aircraft have to monitor aircraft systems, particularly hydraulics, maintain radio communications with ground control and constantly scan for aircraft, vehicles and other obstacles. Just because ground control says you’re cleared to taxi, of course, doesn’t mean that you can be any less vigilant for potential hazards.
So while there are risks from towing aircraft, I believe that generally they are less than when mechanics taxi because they can more fully concentrate on their surroundings. I am reminded of when Logan Airport decided to ban aircraft taxiing for maintenance for noise reasons. Although the ban was not intended to reduce ground damage, anecdotally, it was reported to me that it had a noticeable impact on ground damage reduction.
Although, I believe that towing aircraft is generally a lower risk than taxiing, it may not always be feasible to tow an aircraft for maintenance. In those situations, only mechanics with proper training and experience should be used. And emphasis needs to be placed on all the critical pieces of safe taxiing – maintaining proper speed, monitoring hydraulics, maintaining radio contact and scanning for obstacles.