Set the TO DATA SET MENU to ALL on the MCDU when icing is possible, specifically when OAT is below 5°C with visible moisture

Let me ask you something practical: on a chilly takeoff morning, what tweaks do you make in the cockpit to keep performance honest and safe? If you’ve flown the ERJ and spent time with the MCDU, you know the answer can be found in a small, deliberate setting—the TO DATA SET MENU. It’s not glamorous, but it’s where ice risk gets translated into real-number performance data you can trust.

Here’s the thing about icing. When the Outside Air Temperature (OAT) slips toward the freezing line and there’s any moisture in the air, ice can start forming on surfaces that matter most for flight—think wings, slats, and engine inlets. Ice isn’t just a beauty problem on a wing; it changes shape, adds weight, and subtly robs you of lift. That’s why the crew system includes a way to adapt takeoff data to those tricky conditions. And yes, the TO DATA SET MENU should be set to ALL, but only under the right weather circumstances.

What “ALL” actually does, in plain terms

On the ERJ, the MCDU’s takeoff data block is where the flight computer draws numbers for things like thrust setting recommendations, V-speed calculations, and tailplane considerations. When you set the TO DATA SET MENU to ALL, you’re telling the system to factor in a broader range of conditions—specifically, the potential for ice contamination on takeoff surfaces. The result is performance data that reflects the possibility of icing effects, helping you avoid optimistic numbers that could lead to a too-optimistic takeoff, or a misjudged rotation airspeed.

Now, the big moment: when to flip that switch to ALL

The correct circumstance is pretty exacting: OAT below 5°C with visible moisture. It’s not about being chilly or just “feeling winter.” It’s about a real moisture presence—fog, mist, drizzle, wet snow, or visible moisture on the ramp—that can freeze as the air cools. In other words, conditions scream “be careful” and you’re logically nudged to bring more conservative performance data into play.

If you’re wondering about the other temperature ranges, you’re not alone. The other options—OAT above 10°C, or OAT between 5°C and 10°C, or simply “on the ground”—do not adequately capture the icing risk profile. In warmer weather, or in dry air, the ice hazard isn’t the same animal, so the full ALL data set isn’t necessary. And on the ground, you’re not yet in the air where ice formation affects lift and drag in flight. In plain terms: the icing risk lives in that crisp, subfreezing window with moisture, and that’s exactly when ALL belongs on the display.

Why this matters in real flight, not just theory

Think about it this way: the aircraft’s performance isn’t just about horsepower and fuel flow. It’s about how ice changes the aerodynamics and the engine’s breathing. If you don’t adjust the takeoff data to account for potential ice, you might end up with inaccuracies in required V1, VR, and V2. Those speeds aren’t glamorous numbers; they’re the guardrails that help you rotate safely and climb without fighting a surprise stall or a yaw that you didn’t anticipate.

A practical mindset for when icing risk is on your radar

• Check the forecast and the TAT/Moisture indicators before taxi. If the OAT dips below 5°C and moisture exists—visible moisture, fog, or even light drizzle—you’re in the territory where ALL matters.

• Verify the MCDU setting as you prepare for takeoff. If the weather has improved and the air is dry or above freezing, you may revert to a standard data set, but don’t assume—verify.

• Don’t treat the setting as a one-and-done fix. If you enter a different weather regime or conditions change on the way to the runway, reassess.

A quick, friendly checklist you can tuck into a preflight routine

• Confirm OAT at the cockpit display and on ATIS/flight plan weather pages.

• Observe for visible moisture (persistence of fog, dew, frost, or wet runways with freezing potential).

• If OAT < 5°C with visible moisture, set TO DATA SET MENU to ALL.

• If conditions are marginal but moisture is minimal or absent, discuss with the crew whether the ALL setting remains warranted or if a more conservative approach is needed.

• After takeoff, monitor performance and be prepared to adapt if icing conditions persist or worsen.

A few notes about the craft of flying in icing-prone environments

Icing isn’t just a single-event hazard; it’s a spectrum. Light glaze can add a surprising amount of drag, while rime ice on inlets and wings can change airflow in abrupt ways. That’s why the industry built this data-set switch into the MCDU in the first place. It’s not about sensational issues; it’s about consistent, conservative planning that translates into smoother air and safer climbs.

Think of it like driving in winter. If you’re cruising on a highway with slick patches, you slow down, test your traction, and sometimes switch to a mode that pays closer attention to grip and stopping distances. On the ERJ, the TO DATA SET MENU works in a similar spirit. It doesn’t make the ice disappear, but it helps the flight deck see around the corner with numbers that reflect reality rather than wishful thinking.

A touch of realism—and a hint of humility

No single setting guarantees a flawless takeoff in every icy morning. Weather is messy, and ice can form in unexpected places. The value of the ALL setting is predictive rather than magical. It’s a safeguard that aligns the data with the situation you’re in, helping you pick the right performance parameters and reduce the chance of surprise.

If you’re curious about the broader picture, you’ll see this same philosophy echoed in other cold-weather procedures. Deicing routines, holdover time planning, and performance charts all live in that same space: grounded in the weather, careful in planning, and deliberate in execution. The MCDU knob is just one of several tools that help you translate weather reality into a safe, efficient takeoff.

Dispelling a couple of common myths

• Myth: If it’s cold, I should always set ALL. Reality: Not always. If there’s no visible moisture and the OAT isn’t flirting with freezing, the ALL setting might not be necessary. It’s a conditional tool, not a default toggle.

• Myth: Once I’ve set ALL, I never touch it again. Reality: Weather isn’t a static thing. If the environment shifts, stay attentive and adjust. The goal is to keep the performance data honest in real time.

What this means for you as a SkyWest ERJ crew member

The practice of tweaking the MCDU data set to reflect icing risk is a small but meaningful piece of a larger safety mosaic. It combines weather awareness with precise performance calculation, two elements that distinguish disciplined crews from the rest. It’s about situational intelligence—the ability to translate what you see and what you’re told into safe, predictable outcomes.

So, next time you’re faced with a chilly morning, take a moment to look at the OAT and the moisture picture, then check the MCDU. If conditions meet that specific threshold—OAT below 5°C with visible moisture—set the TO DATA SET MENU to ALL. It’s a quiet, effective step that keeps your numbers honest and your takeoff margins comfortable.

Closing thought

In aviation, as in life, there are moments when tiny decisions ripple outward. The choice to set ALL under the right icing conditions is one of those moments. It’s not dramatic, but it’s precise. It’s the kind of detail that separates routine sorties from consistently reliable operations. And when you factor it into a calmly executed preflight, you’re not just flying—you’re flying with a little more confidence, a touch more clarity, and a safer outcome for everyone on board.