NTSB Safety Alert SA-072 - Minding Weight and Balance

SAFETY

ALERT 072 February 2018

HIGHWAY

MARINE

RAILROAD

PIPELINE

AVIATION

Minding Weight,

Maintaining Balance

Improper or Unperformed Calculations Can be Fatal

The problem

Between 2008 and 2016, the probable causes of

136 general aviation (GA) accidents were related to

pilots improperly conducting preflight performance

calculations for weight and balance or not conducting

them at all. One-third of these accidents resulted in

pilot and/or passenger deaths.

If pilots do not perform preflight calculations to verify

that their aircraft are within allowable weight and center

of gravity (CG) limits, the aircraft could be operated in

exceedance of their certificated takeoff gross weight

and/or outside CG limits.

Overloading aircraft or operating outside of the CG

limits can severely degrade an aircraft’s performance

characteristics and ultimately lead to an aerodynamic

stall and/or loss of aircraft control, typically during

takeoff or landing.

Not accounting for atmospheric conditions—such as

wind, high temperature, and high-density altitude— on

an aircraft’s performance can exacerbate the effects

of operating outside of weight and CG limits. Even if

an aircraft is under or near its maximum gross takeoff

limit, atmospheric conditions can degrade the aircraft’s

performance enough to prevent it from attaining or

maintaining a climb.Related accidents

The following examples from the National Transportation

Safety Board’s (NTSB) accident database show the diverse

circumstances under which these types of accidents

happen:

An airline transport pilot was conducting a flight from

a fishing lodge to a remote fishing location in a float-

equipped de Havilland DHC-3T (Otter) airplane, which

impacted tundra-covered terrain just after takeoff from

a lake. Three passengers were killed, the pilot and four

passengers sustained serious injuries, and two passen-

gers sustained minor injuries. According to a witness,

after liftoff, the airplane began to climb and then de -

scended. The floats struck the water, then the airplane

briefly became airborne again before crashing. The pilot

reported that, before departure, the front and center fuel

tanks were filled and that the aft fuel tank had “residu -

al” fuel. He said that he “guesstimated” the airplane’s

weight and balance before departure (he did not weigh

the cargo, obtain passenger weights, or document any

weight and balance calculations). A postaccident weight

and balance study using the passenger weights, weighed

cargo, and fuel load showed that the airplane exceeded

its maximum gross weight by about 508.6 lbs and that

the CG was 4.08 inches aft of the aft CG limit. The pilot’s

failure to determine the airplane’s actual preflight weight

and CG led to the airplane being operated outside of its

2 / NTSB Safety Alert 072 / February 2018weight and CG limits, preventing it from attaining a prop-

er airspeed and ultimately resulting in an aerodynamic stall. (ANC15FA071 )

A Robinson R22 Beta II helicopter sustained substantial

damage when it collided with rising terrain 10 miles west of its departure point (see figure 1). The private pilot sustained a serious injury, and the passenger sustained a minor injury. The pilot reported that, as he was flying the helicopter up a canyon and climbing in rising mountainous terrain, he no -

ticed a substantial tail -

wind gust, followed by a decrease in air-speed below effective translational lift. The helicopter stopped climbing, and the pi -

lot immediately made a left turn with the intention of reversing course and turning into the wind. Howev -

er, the helicopter impacted rising terrain. The investigation determined that the helicopter was operating about 30 lbs above its maximum gross weight and that the calculated density altitude was about 9,600 ft. The pilot did not know that the helicopter’s gross weight was greater than its maximum due to inadequate preflight planning. His sub -

sequent decision to attempt to climb over rising terrain in

high-density altitude conditions with a tailwind resulted in

the helicopter’s inability to maintain a positive climb rate and subsequent impact with terrain. ( GAA15LA131 )

A Beech 100 ran off the departure end of the runway during takeoff, substantially damaging the airplane (see figure 2). The airline transport pilot, copilot, and eight pas -

sengers were not injured. During the takeoff roll, the air -

plane did not accelerate as quickly as the pilot expected. When the airplane reached the last third of the runway, the pilot pulled back on the control yoke to lift the airplane off the runway, but the stall warning horn sounded. He lowered the nose, but the airplane subsequently departed the runway and impacted terrain and obstacles. The pilot reported that he knew that the total weight of the eight passengers, their bags, and the fuel caused the airplane to be overweight, but he did not complete a weight and balance form or determine the expected takeoff perfor -

mance before the flight (figure  3 shows the unweighed luggage on board the airplane). After the accident, the pi -

lot determined that the airplane was 623 lbs over its maxi -

mum gross weight. The pilot’s decision to depart knowing that the airplane was over its maximum gross takeoff weight was unsafe. Coupling that decision with the pilot’s failure to determine the expected takeoff performance re-sulted in the airplane not accelerating as expected and its subsequent runway excursion. ( CEN17LA029 )

A flight instructor and student pilot were conducting an instructional flight in an Aeronca 11AC airplane when it impacted trees at the departure end of the runway, re -

sulting in minor injuries to the student. The flight instruc -

tor reported that, during the takeoff climb from a grass runway, the “climb rate became stagnant.” He added that he instructed the student to “lower the nose slightly,” but the airplane still could not establish a “normal climb rate.” After taking over the flight controls, the flight instructor turned the airplane toward a small gap in the tree line ahead, and the airplane subsequently impacted the trees. According to the flight instructor, the airplane departed “loaded at gross weight.” The student reported that the flight instructor did not discuss the airplane’s weight and balance with him before the flight. Postaccident weight and balance calculations revealed that the airplane was 139 lbs over its maximum gross weight, and the calcu-lated density altitude was about 2,648 ft. The airplane’s overweight condition, in combination with the takeoff in

high-density altitude conditions from a turf runway, de -

creased the airplane’s takeoff performance and resulted in the accident. ( GAA17CA347 )

Figure 1. Photograph of

substantial damage to Robinson R22 Beta II helicopter

Figure 2 (top). Postaccident

photograph of damaged Beech 100

Figure 3 (at right). Photographs

showing unweighed baggage on Beech 100

NTSB Safety Alert 072 / February 2018 / 3

What can pilots do?

Know your aircraft’s limitations and the factors

that can affect its performance.

Conduct weight and balance calculations in

accordance with the applicable aircraft flight

manuals (AFM) to ensure that your aircraft is

loaded within its weight and CG limits. The

limitations section of each AFM or Pilot’s

Operating Handbook contains details about the

maximum weight and CG limits for takeoff and

landing.

Be prepared and conduct takeoff and landing

distance calculations as part of your preflight

planning. Remember to account for fuel burn

during flight, which will result in a CG shift and

decrease in weight.

Be aware of the atmospheric conditions that

exist at the time throughout your flight and

account for these factors in all your performance

calculations.

Remember that operating the aircraft above

its maximum gross weight can result in a

longer takeoff run due to the airplane’s slower

acceleration and the need for a higher takeoff

speed; shallower climb angles and reduced climb

rates; reduced cruising speed; shorter range;

higher stall speeds; and longer landing rolls.

Be aware that operating an aircraft outside of

its CG limits can degrade its handling qualities,

resulting in reduced stability and/or reduced

control authority, which increases the risk of a

loss of control. Be vigilant on every flight. Determine the CG even if your aircraft is under

its maximum gross weight. Even if an aircraft

is within its allowable gross weight, it may be

loaded outside of its CG limits.

Do not “guesstimate” passenger and cargo

weights. The margins of error are small, and even

slightly underestimating these weights could kill

or seriously injure you, a friend or colleague, or a

family member.

When using automated weight and balance

application calculators, ensure that the basic

empty weight and moment match the specific

values for your aircraft. Sample weight and

balance data should never be used as a substitute

for actual numbers in the AFM.

If any major modifications to your aircraft change

its weight or CG, such as the installation of

onboard equipment, ensure that this information

is in the updated weight and balance forms

contained in the AFM.

Remember that aircraft performance can only be

determined after the gross weight is computed.

Professional flight crews do these computations

routinely. You should strive for professionalism

as well when you are planning your flights.

REMEMBER — Before Every Flight,

Ensure That Your Aircraft

Can Operate Safely

4 / NTSB Safety Alert 072 / February 2018Interested in more information?

Education and training are essential to improving GA

safety. The Federal Aviation Administration (FAA) Safety

Team (FAASTeam ) provides access to online training

courses, seminars, and webinars as part of the FAA’s

“WINGS—Pilot Proficiency Program.” The program

includes targeted flight training designed to help pilots

develop the knowledge and skills needed to achieve

flight proficiency and to assess and mitigate the risks

associated with the most common causes of accidents,

including operating outside of weight and CG limits. The

courses and resources listed below (among others),

as well as seminar and webinar information, can be

accessed from the FAASTeam website at account or

creation of a free FAASTeam account.)

• Performance Limitations

• Helicopter – Weight & Balance, Performance

• Weight and Balance P-8740-05FAA-H-8083-1, “ Weight and Balance Handbook,” and

FAA-H-8083-21A, “ Helicopter Flying Handbook ” both

provide pilots with information on loading and operating

aircraft and emphasize the importance of ensuring

that the weight and CG are within the allowable limits.

The handbooks also describe the negative effects of

overloading an aircraft and operating an aircraft outside

of CG limits. The handbooks provide exemplar loading

computations for GA aircraft and corresponding loading

graphs and tables of weight and moment indexes. Both

handbooks can be accessed from the FAA’s website at

www.faa.gov.

A companion video to this safety alert can be accessed

from the Aviation Safety Alerts link.

The reports for the accidents referenced in this safety

alert are accessible by NTSB accident number from the

Aviation Accident Database link, and each accident’s

public docket is accessible from the Accident Dock ets

link for the Docket Management System.

The NTSB’s Aviation Information Resources web page, www.ntsb.gov/air ,

provides convenient access to NTSB aviation safety products. This Safety

Alert and others can be accessed from the Aviation Safety Alerts link at

www.ntsb.gov .

The NTSB is an independent federal agency charged by Congress with investigating every civil aviation

accident in the United States and significant accidents in other modes of transportation—highway, marine,

railroad, and pipeline. The NTSB determines the probable cause of the accidents and issues safety

recommendations aimed at preventing future accidents. For more information, visit www.ntsb.gov .www.twitter.com/ ntsb

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