Rules citation? Flight and carrying capacity

[CronoDekar]

It is an inference, but one of the things I think is added that helps make it clear is the quote from MM 312 is "(Note that medium armor does not necessarily constitute a medium load)." Since having medium armor and a medium load both normally affect speed the same way, it would be odd that they would bother making this note.

Additionally, DMG 205 lists alternate paladin mounts. The first note for the table says "A creature capable of flying as well as ground-based movement uses the carrying capacity on the first line of its entry if it is flying. If it is not flying, the carrying capacity on the second line of its entry applies." Looking at, for example, the Hippogriff, its light load is 300 lb and its max load is 900, which matches up with the table figures.

I think the fly spell is mainly meant as the exception, primarily so the caster isn't limited to only being able to effectively casting the spell on those with a light load in the party.

 

[Iku Rex]

Where does it say that?

Did you not check the cites I provided?

How about a FAQ answer?

Q:The entry on flight in the Monster Manual doesn’t elaborate
on whether carrying a medium or heavy load actually
prevents flight, or it simply slows the flyer down below the
indicated speed (and in the latter case, it doesn’t explain by
how much the creature is slowed down). Some of the
monster entries do make mention of medium and heavy
loads in terms of carrying capacity (griffins and spidereaters,
for example). Does that mean those creatures can fly
with medium or heavy loads? Is it even possible for a flying
creature to get airborne at less that its listed fly speed.

A: You can use a fly speed only when carrying a light load or
less. If your load is medium or heavy, you cannot fly; certain
kinds of magical flight, such as a fly spell, don’t have this
restriction. Check the description of the flying effect to be sure.
A griffin or a spider-eater can carry a medium or heavy
load, but it cannot fly when doing so.
Most flying creatures can get aloft at less than their full fly
speeds, provided that they can maintain their minimum forward
speeds (see Tactical Aerial Movement in Chapter 2 of the
Dungeon Master’s Guide). You also can fly when wearing
medium or heavy armor if the weight of the armor (plus
everything else you carry) doesn’t exceed your light load
rating. The armor still slows you down (page 20 in the
Dungeon Master’s Guide has an expanded table of reduced
speeds). For example, a balor is a Large creature with a
Strength score of 35. A light load for a balor is 2,128 pounds.
To calculate that, we must use the tremendous Strength rule on
page 163 of the Player’s Handbook and find the light load
rating for Strength 25 (the number between 20 and 29 that has
the same 1’s digit as 35). This gives us a value of 266 pounds.
Since the balor’s Strength is 35, we multiply 266 by 4, which
gives us 1,064 pounds. The balor is a Large biped, however, so
its carrying capacity doubles (1,064 x 2 = 2,128). A balor can
fly so long as it carries less than 2,128 pounds. A breastplate
for a Large biped weighs 60 pounds (from Table 7–6 in the
Player’s Handbook), so its weight won’t keep a balor from
getting aloft when wearing it. Since a breastplate is medium
armor, the balor’s base fly speed of 90 feet is slowed to 60 feet
(from the table on page 20 of the Dungeon Master’s Guide).
Since the balor has good maneuverability, it has no minimum
forward speed and can easily fly wearing the breastplate. Even
if the balor had poor maneuverability, its minimum forward
speed would be 45 feet (half its base speed of 90 feet), and it
still could fly at a speed of 60 when wearing the breastplate.
If a creature’s base flying speed is greater than listed on the
chart on page 20 of the Dungeon Master’s Guide, just divide
the creature’s base flying speed into equal parts dividable by 10
and then add up the reduced values for those base speeds off
the chart. For example, if a flying creature with a fly speed of
150 feet wears medium armor and can still get aloft, it can fly
at a speed of 105 feet. (Its minimum forward speed, if it had
one, would be half the base flying speed, or 75 feet.) The
reduced speed of 105 feet was calculated by splitting the fly
speed into 70 feet and 80 feet (70 + 80 = 150). At reduced
speed, 70 feet becomes 50 feet and 80 feet becomes 55 feet (50
+ 55 = 105).
Note that some creatures in the game cannot fly when
wearing medium or heavy armor, no matter what their load
happens to be (for example, the avariel from Races of Faerûn),
so be sure to check the creature’s description for any special
limits on its flying ability.

 

[frankthedm]

The No flight at medium or heavy load was created by wotc in the "defenders of the faith book back in 3.0 IIRC. Before this i do belive only heavy load prevented flight IIRC.