April 2004 Volume 47 / Number 4
Bruce Landsberg, ASF executive director, has had more than a few surprises on first flights after maintenance.
This column is not about the trials suffered by the brothers Wright to bring us into the age of aviation but rather a reminder to be suspicious of any aircraft when it is returned to service from any maintenance encounter. A significant problem may rear its head right at the point of rotation, requiring immediate action to prevent catastrophe, and sometimes a forced landing is inevitable. First flights after maintenance always should be considered possible high-risk events.
Aviation maintenance technicians, as a whole, are outstanding and our safety record reflects that. Pilots are far more likely to be the architects of their own disasters, but techs do have an awesome responsibility and, like medical doctors, might take the Hippocratic oath, "First, do no harm," then see if you can fix the problem. We've all had experiences where a car, aircraft, lawn mower, you name it, went into the shop with a minor crisis and left in much worse shape. It's not deliberate but the outcome, especially in aircraft, can be more than inconvenient.
Sometimes there is nothing the pilot can do. A Cessna 210 pilot reported a malfunctioning indicator light and put the aircraft into the shop. On the first flight the landing gear failed to retract. The pilot returned to the airport but on touchdown the right main gear collapsed. An examination revealed a loose wire in the landing gear handle, which sent a false indication to the right main gear actuator switch, causing the system to unlock but not initiate landing gear retraction. A small indication problem turned into a real "aw-shucks" as a result of trying to troubleshoot and fix something else.
A good procedure is to have an experienced pilot fly the aircraft after any significant maintenance to verify proper operation, but sometimes the gremlins attack too quickly. The carburetor on a flying club Cessna 172 was replaced a week prior to the accident, but the airplane had experienced several "abnormal events" since its installation.
According to the pilot — who was the club maintenance officer returning the aircraft to the shop for a review of the problem — the engine runup and liftoff were normal. At 300 feet the engine ran rough for about 10 seconds, then lost all power. The pilot executed a forced landing into the only grass area in the vicinity, but the airplane struck a gas pipeline, causing significant damage but no fire. The mixture control cable was not secured to the mixture control arm pivot bolt. A review of the maintenance records revealed the carburetor was replaced with the entry stating, "Set idle speed and mixture to specs."
An extra thorough preflight after maintenance is always a good idea. Rags, wrenches, old parts, disconnected hoses, and wires are just some of the detritus sometimes left behind. The transgression can be a misdemeanor or a capital offense. Most of the better shops, the airlines, and the military use tool inventories, like surgeons, to be sure nothing is left inside the patient. Besides, it's really aggravating for a tech to leave a seven-sixteenth-inch six-point socket inside one aircraft and need it for the next job.
Several areas fall into the big-deal category. Anything involving flight controls, the engine, or the fuel system has the potential to create major mischief. When the rigging or control surfaces have been in for adjustment or maintenance, be on high alert that something may go radically wrong. There have been several high-profile accidents, including two involving Beech 1900 regional airliners that crashed in 2003 with the preliminary indication of misrigged controls after maintenance. One involved maintenance on the trim tab and a possible overweight/out-of-balance condition. The other had recent maintenance on elevator trim actuators and a possible runaway trim malfunction. Both are in preliminary status and this information may change.
Another Beech 1900 was saved by quick response. As the airplane accelerated to 115 knots, about V1, the captain noted that the elevator control was jammed and successfully aborted the takeoff. The post-incident examination revealed that when the elevator trim wheel in the cockpit was positioned to neutral, the elevator trim was actually in a nose-down position. The incident occurred on the first flight after maintenance, which included removal and replacement of a throttle pin. The elevator trim wheel had to be removed, but the mechanic did not index the elevator trim wheel before removing it and reinstalled it incorrectly.
A Beechcraft Debonair that I used to fly broke a fuel-injection line, and the safety conscious owner decided that all the lines should be replaced. The shop performed the change and the owner, a retired naval aviator and maintenance officer, insisted on flying the Deb first. After a normal runup and just after liftoff, the engine surged and started to lose power. The owner immediately aborted and slid off the end of the runway, carefully avoiding the localizer antenna and some runway lights. There was no damage to the aircraft, but the nut that secured the main fuel line to the fuel distributor had not been tightened so the engine was well washed in 100 octane.
Recently overhauled engines have great potential for mishap. On the Piper Arrow's initial flight test, the climb-to-cruise altitude of 3,000 feet agl was accomplished "with no difficulty." Eight minutes into the flight, the engine rpm increased to redline and, as the pilot adjusted the propeller control to compensate, the engine stopped. A forced landing ensued with no injury but with substantial damage to the Piper. Investigation showed that one oil pressure fitting in the engine accessory drive case had not been capped.
A new twist on first-flight fiascos comes with the navigation database updates that many airplanes now require. As with human surgery where there is always the possibility of infection, so it is with databases. The AOPA Air Safety Foundation's Piper Archer, which has a sophisticated GPS navigator, caught the crud during a routine database update. I was first to fly after the operation and found the heart of the navigator to be DOA. It was just a short VFR hop but if IFR had been required, the flight would have been ill-advised. As a result, we've altered our update procedure so that whenever a database change occurs the unit is immediately powered up to verify that all the bits and bytes are behaving as expected.
This issue becomes ever more important as the transition to integrated glass cockpits continues. The primary flight display, navigation page, waypoint information, and database access paths all may be configured differently from where you last left them if someone else has flown or worked on the aircraft. Selecting the wrong mode is a new problem for light GA that has been with the airline and corporate crowd for years. Add a new line to your predeparture checklist — nav source (GPS or VOR/LOC) verified.
Accidents trigger investigations and at least some publicity, but many maintenance miscues never cause an accident and never hit any statistical database, so we probably only have a small part of the picture. The bottom line on first flights after maintenance is to be cautious. Choose long runways with good overruns, if possible. Gain altitude quickly and keep a landing site readily available. Don't carry nonessential passengers, but do take the tech who just signed off the aircraft as airworthy — that's evidence of good faith. Keep all this in perspective — most of the time the shop will have done the job correctly and everything will go as planned — but it wouldn't hurt to remember your tech's birthday.