Decision Altitude Versus Minimum Descent Altitude, the One Word That Changes How You Fly the Bottom of an Approach

The difference between a Decision Altitude (DA) and a Minimum Descent Altitude (MDA) comes down to one word. A DA belongs to a precision or vertical-guidance approach and is a decision point you descend through as you choose to continue or go around. An MDA belongs to a non-precision approach and is a hard floor you level off at and never go below unless the runway is in sight for a normal landing.

Both numbers do share one job: each is the lowest you are allowed to go on an instrument approach unless you can see what you need to see to keep descending to the runway. They sit in the same minimums box, in the same font, on the same chart. The split is entirely in how you use that floor.

What Is a Decision Altitude (DA)?

A Decision Altitude belongs to a precision approach, or what is now more broadly called an approach with vertical guidance. Think of an ILS (Instrument Landing System) or an LPV, the satellite-based approach that flies like an ILS. On these, you follow a glidepath - a continuous descending electronic ramp that tells you both left/right and up/down all the way down.

The key word is decision. When you reach the DA, you decide: continue if you have the runway environment in sight, or go around if you don’t.

Here is the part most people miss. You are allowed to descend through the DA while you make that decision. Because you are flying a continuous descent on a glidepath, you cannot freeze the airplane at an exact altitude. When you hit DA without the runway in sight, you begin the go-around right then - and in the second or two it takes to arrest the descent and start climbing, you will dip slightly below the DA. That is expected, normal, and built into how the approach is designed.

The DA is a decision point you pass through, not a hard deck you are forbidden to cross.

What Is a Minimum Descent Altitude (MDA)?

A Minimum Descent Altitude belongs to a non-precision approach - an approach without vertical guidance. Think of a localizer-only approach, a VOR approach, or an LNAV (lateral navigation only) off the GPS. These tell you where you are left and right, and they tell you not to go below a certain altitude, but there is no glidepath needle pinning your vertical path.

The key word is minimum. That is a floor you do not bust. Period.

You descend to the MDA, level off, and fly straight and level toward the missed approach point, looking for the runway. You do not go below the MDA unless you have the runway environment in sight and you are in a position to make a normal landing. If you reach the missed approach point and still can’t see what you need, you go missed from at or above the MDA - you never dip below it hoping the runway will appear.

The MDA is a hard floor you sit on.

Why the Difference Matters When You’re Flying

This affects you most on the day two approaches to the same runway have very different minimums.

Picture a field with an ILS to one runway and a localizer-only approach to that same runway. The precision ILS might get you down to 200 feet above the touchdown zone with a Decision Altitude. The localizer approach - same runway, same airplane - might have an MDA that leaves you 500, 600, or 700 feet up, sometimes more.

The reason is trust. The precision approach gives you vertical guidance all the way down, so the system lets you go lower. The non-precision approach doesn’t, so it holds you higher, hands you a floor, and makes you look for the runway from that floor. Same weather, same runway - the kind of approach you fly can be the difference between landing and diverting.

On a non-precision approach, leveling off at the MDA means you are trading altitude for time. The sooner you can safely get down to the MDA, the more time you spend scanning for the runway before the missed approach point. That is why many instructors teach getting down to the MDA promptly and cleanly - level off, get stable, get your eyes outside, and use every second.

By contrast, on a DA approach you are not leveling off and hunting. The airplane does one thing - a stable descent on the glidepath - right up until the decision arrives at a specific altitude.

The Constant Descent Final Approach (CDFA) Caveat

Many pilots now fly non-precision approaches using a constant descent final approach (CDFA), also called a stabilized approach. Instead of dropping to the MDA early and driving along level, you compute a steady descent timed to arrive at the missed approach point right at the MDA - flying it much more like a precision approach. It is smoother and safer, and it cuts down on the “dive-and-drive” habit that has bitten pilots over the years.

But here is the catch: the MDA is still a hard floor. If you fly a continuous descent aiming at the MDA and arrive without the runway in sight, you go missed - and in that transition you could sag below the floor.

So pilots flying this profile build in a small buffer, sometimes called a derived decision altitude, so they make the decision a hair early and never bust the minimum. Even flown with a smooth, precision-style descent, an MDA does not become a DA. The rule about the floor does not change; you just fly it smart so you never touch it.

What You Should Actually Do About It

Know your number before you brief. Look at the minimums box and confirm whether it is a Decision Altitude or a Minimum Descent Altitude - because it changes what you do the instant you get there. Decide that on the ground, not at 200 feet in the clouds.

Choose the right approach for the weather. If you have a choice of approaches to the same runway and the weather is right down on the deck, the precision or vertical-guidance approach with its DA will very often give you lower minimums and the better shot at getting in.

Respect the floor on a non-precision approach. Level off at the MDA, or fly a stabilized descent with a buffer, but never go below it on a hope. The runway environment in sight, in a position for a normal landing, is the only thing that lets you continue down. Otherwise it’s the miss, from at or above that altitude, every time.

One word - Decision versus Minimum. Pass through it, or sit on it.

Key Takeaways

• A Decision Altitude (DA) applies to precision/vertical-guidance approaches (ILS, LPV); you descend through it to decide, and a momentary dip below during the go-around is normal.
• A Minimum Descent Altitude (MDA) applies to non-precision approaches (localizer, VOR, LNAV); you level off at it and never descend below it without the runway in sight.
• Precision approaches typically offer much lower minimums - a DA near 200 feet versus an MDA that can leave you 500–700+ feet up on the same runway.
• Going missed on a non-precision approach must happen at or above the MDA, never below it.
• When flying a constant descent final approach (CDFA), add a buffer (a derived decision altitude) so a continuous descent never busts the MDA floor.