Load factor and density altitude on the Part 107 test
Loading and performance is the smallest area on the Part 107 test: 7 to 11% in the FAA’s Airman Certification Standards, and 2% under PSI’s current weighting. Density altitude sits under weather, which is 11 to 16% in the ACS and 5% at PSI.
Small doesn’t mean skippable. There are only a handful of concepts to learn, and the same ideas explain why a drone loses performance on a hot afternoon at a high job site.
Load factor
Load factor is the ratio of the load on an aircraft’s structure to its weight, measured in Gs. A load factor of 3 means the structure carries three times the aircraft’s weight. Any force that bends the flight path away from a straight line adds load.
The FAA Remote Pilot Study Guide gives two reasons it matters. A pilot can overload the structure, and a higher load factor raises the stall speed, so a stall can happen at a speed that seems safe.
Load factor in a level turn
In a coordinated turn at constant altitude, the load factor depends only on the bank angle. It climbs slowly at first and steeply past 45° to 50°.
| Bank angle (level, coordinated turn) | Load factor |
|---|---|
| 60° | 2 G |
| More than 72° | 3 G |
| 80° | 5.76 G |
The Study Guide adds that a level turn at 90° of bank is not mathematically possible, which is why the curve never reaches that line.
If you remember one row for the test, remember 60° equals 2 G.
Load factor and stall speed
Stall speed goes up with the square root of the load factor. The Study Guide’s examples:
- An aircraft that stalls at 50 knots in unaccelerated flight can stall at 100 knots at 4 G (the square root of 4 is 2, and 50 times 2 is 100).
- In a turn steep enough to reach 3 G, an aircraft with a 45-knot stall speed must stay above 75 knots to avoid stalling.
The same effect happens in a quick pull-up or any maneuver above 1 G. The Study Guide notes that this sudden loss of control near the ground has caused many accidents.
For a fixed-wing drone this is directly practical: steep turns at low speed are where stalls happen. On the test, the words “steep turn,” “bank” or “pull-up” are your cue that load factor, and so stall speed, has gone up.
Density altitude
Density altitude is the altitude in the standard atmosphere that matches the air density you actually have. The handbook defines it as pressure altitude corrected for nonstandard temperature. The aircraft performs as if it were at that altitude, whatever the altimeter says.
Two reference points help:
- Pressure altitude is what an altimeter reads with its setting at 29.92 inches of mercury.
- Standard atmosphere at sea level is 29.92 inches of mercury and 15 °C (59 °F).
High versus low
High density altitude means thin air, and aircraft performance decreases. Low density altitude means dense air, and performance increases.
| Condition | Effect on density altitude | Effect on performance |
|---|---|---|
| High elevation | Raises it | Decreases |
| Low atmospheric pressure | Raises it | Decreases |
| High temperature | Raises it | Decreases |
| High humidity | Raises it | Decreases |
| Low elevation, high pressure, low temperature, low humidity | Lowers it | Increases |
Why humidity counts
It seems backwards, but moist air is lighter than dry air because water vapor is lighter than air. More water vapor means less dense air, higher density altitude and less performance. The handbook says there’s no rule of thumb or chart for the humidity correction, but you should expect lower performance in humid conditions.
The worst case is hot, humid and high. Warm, moist air at an elevated site gives the highest density altitude and the weakest performance.
The FAA’s own sample questions include one on what high density altitude does to a UA propeller’s efficiency. Work it from the principle above: thinner air, less performance.
Loading and balance
AC 107-2A’s supplemental guidance on loading gives the rules the ACS tests under loading and performance:
- Check weight and balance before every flight and follow the manufacturer’s limits.
- Maximum gross weight isn’t always safe. High elevation, high temperature and high humidity (high density altitude) can require a lighter load before takeoff.
- Weight can change in flight. Releasing a jettisonable load makes the aircraft lighter, which helps performance but can upset balance.
- The center of gravity moves as loads shift or are used up. If it’s outside limits, relocate or remove weight before flying.
Part 107 adds two hard rules. The aircraft must weigh less than 55 pounds at takeoff including everything attached. During preflight, you must make sure any attached or carried object is secure and doesn’t affect the flight characteristics or controllability.
Weight and climb
The Study Guide explains why weight hits climb performance so hard. Add weight, and the aircraft needs a higher angle of attack to hold the same altitude and speed. That adds drag, which leaves less reserve thrust for climbing. Climb performance also shrinks as altitude increases, so a heavy aircraft at a high site gets both penalties at once.
AC 107-2A also notes that manufacturer performance data isn’t standardized. If yours publishes none, the AC suggests starting from data other operators of the same model have published.
Quick checks before test day
- Does a hotter day raise or lower density altitude? Raise.
- Does humid air help or hurt performance? Hurt, because moist air is less dense.
- What is the load factor in a level 60° bank? 2 G.
- What happens to stall speed as load factor rises? It increases, with the square root of the load factor.
- Where does a jettisoned load cause trouble? Balance, as the center of gravity shifts.
Putting it together
Picture a summer afternoon inspection at a high-elevation site with humid air and a heavy camera payload. Every factor points the same way: high density altitude, reduced performance, and a load that may need trimming. If the flight also calls for tight banked turns in a fixed-wing aircraft, the load factor raises the stall speed on top of that.
That scenario covers most of the questions in this area. Weather reports feed into it too, since temperature and altimeter setting come straight from a METAR. See METAR and TAF decoding for Part 107. Worked example 3 in Part 107 practice test questions, explained is a load factor question in test format.
Check yourself on the free practice test, which scores each test area separately.