In everyday flight operations, some pilots look at weight and balance limitations as gospel. Others look at them as mere guidelines—if the door closes, it’ll fly. And then there are ferry pilots, those who strap down a fuel bladder in place of the rear seats and launch on 12-to-15-hour overwater legs, usually with some paperwork allowing over-gross operations.
Of course, the average personal airplane usually operates well below its gross weight, carrying a pilot, a few bags and full fuel. Every now and then, though, we try to fill all the seats, stuff bags under some of them and then spend quality time with the AFM/POH, determining how far we can go on the small amount of fuel it says we can carry. Inevitably, we’re tempted to fudge things a little—what’s an extra 25 or 50 pounds, as long as it’s within the center-of-gravity (CG) limits? Does it really matter if the fuel burn puts me slightly outside the aft limit at my destination?
Most of the time, being slightly over-gross doesn’t matter that much. While we certainly don’t advocate overloading your flivver, putting aboard a couple of extra pounds usually doesn’t result in a smoking hole off the end of the runway. One of the keys involves making sure the loading remains within the CG envelope throughout the flight. Another is to ensure there’s enough smooth, unobstructed runway and flat terrain under your initial flight path allowing for a slower-than-usual climb.
Getting outside the fore-and-aft CG limits is an entirely matter, however, usually resulting in stability issues. Exceed the forward CG limit and flaring for landing can be problematic. Get beyond the aft limit, meanwhile, and you’ll need a gentle touch on the pitch control. In neither case will the airplane fly as it should.
Above all, secure heavy items to prevent them from shifting in turbulence and making things worse. Although over-gross operations routinely occur—both with and without FAA approval—getting outside the CG limits can easily lead to loss of control. Here’s a great example of what can happen.
Background
On November 25, 2010, at 0628 Pacific time, a Mooney M20R Ovation collided with terrain in a plowed field shortly after takeoff from the Hollister (Calif.) Municipal Airport (CVH). The airline transport pilot sustained fatal injuries and the airplane was substantially damaged. The flight departed CVH at about 0624 with Honolulu, Hawaii, as its planned destination. Visual conditions prevailed; an IFR flight plan had been filed. The flight was due to be the 11-hour-long first leg of an export ferry flight to Australia. The accident airplane was the second in a flight of two. The first airplane departed minutes before the accident flight.
A witness observed the airplane depart but soon lost sight of it. A short time later, she observed a similar airplane flying back toward the airport. The airplane’s nose dropped, then it leveled off. The nose dropped again, but this time the airplane spun to the ground. A second witness recounted a similar observation, and stated that at no time during the flight did the airplane appear to be trailing smoke or vapors.
Investigation
The airplane came to rest in a plowed field four miles northwest of the departure runway. Ground scars and damage to the airplane were consistent with a flat spin. Post-accident examination revealed no evidence of airframe or engine malfunctions precluding normal operation. The throttle control position and the lack of witness marks on the propeller indicated the engine was operating at low power at the time of impact, consistent with the manufacturer’s published spin recovery procedure.
Recorded navigation data indicated the airplane’s takeoff roll required 36 seconds. About 84 seconds after takeoff, the pilot initiated a left turn toward the first waypoint. During the next 47 seconds, the left turn was completed, and the airplane continued to climb to its maximum altitude of about 1500 feet. The airplane then began to descend and about 24 seconds later, reached a groundspeed of 144 mph and entered a second left turn. Over the remaining 79 seconds, the left turn continued with an accompanying series of three diverging groundspeed and altitude oscillations, ending at a groundspeed of 69 mph and an altitude of about 300 feet.
The airplane was equipped with a ferry tank system consisting of a 238-gallon collapsible bladder in the cabin behind the pilot’s seat, which contained about 121 gallons of fuel. The bladder was to be attached to the fuselage with ratcheting straps. A mechanic observed tie-down straps installed over the bladder tank two days before the accident. However, no straps were found at the accident site, and the tank appeared to be unrestrained.
In addition to the extra weight of the fuel in the bladder tank, 187 pounds of unsecured baggage was located behind the tank. Although the ferry system allowed for a one-time, 15-percent increase in maximum gross takeoff weight (MGTOW), the weight of the airplane at the time of the accident was estimated to be about 23 percent beyond MGTOW. Additionally, an estimate of the airplane’s center of gravity position at the time of the accident revealed it was about 0.8 inches beyond the aft center-of-gravity limit. No weight and balance sheet referring to the airplane in the ferry flight configuration was located.
The pilot of the other Mooney stated that prior to departure, the tank in the accident airplane was positioned behind the pilot’s seat, and held in place by the airplane’s sidewalls and luggage in the aft baggage area.
Probable Cause
The NTSB determined the probable cause(s) of this accident to include: “The pilot did not ensure the airplane was loaded within its weight and balance envelope, which resulted in longitudinal instability and a loss of aircraft control during the initial climb.”
The NTSB also noted, “It is likely that the aft loading resulted in the airplane encountering longitudinal instability during the initial left turn and entering a series of altitude and pitch oscillations, which would have been extremely difficult for the pilot to control. Also, the unsecured fuel tank and baggage could have moved during takeoff or after the oscillations began, shifting the center-of-gravity farther aft and exacerbating the longitudinal instability.”
If you’re going to operate at higher-than-gross weight, which we don’t recommend, at least ensure all heavy items—like a bladder tank containing more than 100 gallons of fuel—are properly secured.
