Here are some further tips for players and composers:
For players, when doing air sounds, it is not always necessary to use as much air as possible. After a long, loud passage, you might find yourself passed out on the floor! The trick here is to make as sibilant a sound as possible. One way of doing this is to actually narrow the throat a little to make the air passage smaller (I know, just the opposite of what we all learned!), then raise the tongue a little, so that it disturbs the distribution of air wanting to escape from your mouth. These are subtle adjustments, you needn’t do too much. All you are doing is speeding up the air, as when you narrow the end of a garden hose to make it spray further. For loud passages, you will still need to give extra support from down below, putting your abdominal muscles into play.
The pizzicati sounds will be louder and more resonant if the flute is turned out a bit. The more you can make resonance in your own mouth, the better. For maximum resonance for key clicks, stay in playing position, open your throat as far as possible, and open your mouth just a bit more over the embouchure hole to create an extra resonance chamber.

I have posted some further information on the production of tongue pizzicato here.

For composers:
There is unfortunately no standarisation of notation for these effects. I have shown on the video those recommended by Pierre-Yves Artaud in his book Present Day Flutes. I find these to be quite intuitive, but maybe another flutist will have another opinion.
When notating air sounds for the flute, please avoid using empty note heads, unless an empty note head is rhythmically called for (a half note, dotted half note, or whole note). I know, Helmut Lachenmann, Isabel Mundry, and other well-known composers use open note heads, but it makes their music extremely frustrating to read. I am hoping that this tradition will die out. (For more about this and to see written musical examples, read my blog entry here.)
Key clicks on the flute fall into my “Why Bother?” category. Unless you carefully compose them in a solo work, or under amplification, you won’t  hear them.  95 % of the time, I end up having to reinforce them with a tongue pizz. Helmut Lachenmann’s Mouvement is an exception, there are some passages with pure key clicks that can actually be heard! However,  other passages in that piece that need the reinforcement of a tongue pizz.
Note that the difference between a tongue pizz produced on the palate and a tongue pizz produced on the lips is not very distinct. It may be best to let the player decide where to produce the pizz. Some can do it on the palate better, others more effectively on the lips. However there are circumstances, such as close amplification, where that small difference can be quite interesting.
Now, if only I could beatbox…..

Here are some tips on the use of air or aeolian sounds:
Be sure to specify if you want these sounds:
A. produced in playing position (so the air goes across the flute and produces a pitch that corresponds with the fingers), or
B. produced inside the flute: i.e., if you want the flutist to cover the embouchure hole and produce a kind of unpitched “white noise”.

Sometimes I am asked to produce type “A” with the specification “no discernible pitch”. This is nonsense: if a flutist blows across the flute they will always produce some sort of pitch. Even with no fingers down, you will get something in the neighborhood of C#. If you want unpitched noise, ask to flutist to blow into or inside the flute (cover the embouchure hole). In this position, the flutist can produce a range of unpitched sounds from bright (higher sounding white noise) to dark (lower sounding white noise) by changing the position of the tongue.

This leads to my next point: the use of different vowel sounds for color effects. This is most effective with the embouchure hole covered (type “B”). A good example is Hans Zender’s Lo-Shu II. Vowel sounds are much less marked in normal playing position (type “A”), so be sure to take care in ensemble situations.

Some general thoughts about notation:
There are several notational traditions from the Artaud and Levine books concerning the notation of “aeolian” or “air” sounds which I would like to ask composers to avoid. When composing these sounds especially in a situation where rhythm is crucial (especially in an ensemble situation) please avoid the notation that uses empty note-heads:

This notation makes the distinction between a quarter note and a half note difficult. When a player is reading, this can be very annoying. It’s good to have a different note shape, but be sure to fill in the note head in when needed so the player can read the rhythms easily:

An easy way to indicate a gradual change from normal sound to air is by using text with a dotted line:

or simply with a filled circle connected to an open circle by a dotted line:

I am astonished by the occasional vitriol I encounter from some prominent flutists when it comes to extended techniques such as multiphonics, circular breathing and so on. They chant the same nonsense: “bad for your embouchure”, “waste of time”, “don’t be one of those players”. After over 20 years of experience with these techniques as a player and teacher, I am convinced of their benefit to traditional playing. But that’s not what I want to post about. I would like to approach this question from another angle.

Some years ago in an active network forum a very prominent flutist remarked that flutists who can circular breathe belong to a certain class of players whose time would have been better spent working on learning to play properly. I won’t delve into the implications here. It made me livid. I spent 11 weeks in 1992 learning to circular breathe, did that hinder me from playing properly? How idiotic! This person has somewhat recanted this initial statement, but the shadow of stigma still applies in some circles.

Now I have 5 years experience teaching at the conservatory level, and I’ve begun to understand this attitude. I won’t say I sympathize, but I understand it enough to offer some insights which I hope will help students, teachers and composers. There are two issues, as I see it.

The first is a basic misunderstanding. Here is an illustration – this semester I had a student who was swamped with student ensemble compositions and several 20th century repertoire pieces. After this period, she came to me with an 18th century work. The sound was bad, no focus, articulation stuck, breathing shallow. She had tied herself into knots because of the difficulty of the contemporary works, which included circular breathing, microtonality and switching to alto and bass flutes. A typical teacher’s reaction would be “OK, see what that stuff does to you? No more!” But folks, the music itself is not at fault, it was the student’s attitude toward it that stressed her and put her practice into panic mode, causing physical problems that set her way back.

That can happen with any repertoire. It can happen when you first learn to play the piccolo. Good and balanced practice on the piccolo can help and enrich your flute playing, as can good and balanced practice of extended techniques. Managing the airstream and angle for piccolo playing is also an extention of flute technique. Exercising the same management for multiphonics is not such an “out-there” thing.

It wasn’t for nothing that Aurèle Nicolet always said: “You must play Baroque music every day, you must play Bach every day!” If you practice extended techniques as a true extension of good practice out of good flute technique, you won’t fall back, or at least if you do, the recovery time will be very quick.

However, there is another aggravating element, which leads me to the second point, the disparity between composing and performing. Student composers don’t necessarily need endless years of training to write very complicated music. Student instrumentalists and singers need decades of training before they acheive the level it takes to play a complicated piece it took a student composer only one semester to write. I’ve put this rather crudely but you get what I mean. Since being a composer-performer is not really encouraged by the conservatory system, this artistic link has been severed. Our only hope is diplomacy! Communication of the issues of difficulty is very important. Encouraging an us-versus-them attitude will make the situation for both worse.

When a flute student is first exposed to contemporary techniques at the conservatory level, it is likely s/he will be overwhelmed because that first exposure may be a standard repertoire piece written for a professional [think of all the works written for Pierre-Yves Artaud, Robert Aitken, Roberto Fabricciani and so on], or written by a student or faculty composer who assumes that level as the norm. The student is frustrated, the teacher, if inexperienced, is also frustrated and there’s another black mark against contemporary music. The earlier good, measured, positive exposure to extended techniques, the better.