CASA IREX common mistakes
CASA IREX · Understand the traps and how to avoid them.
When asked to determine the minimum fuel required for an IFR flight, the candidate uses the trip fuel only and ignores the reserve, alternate, and contingency fuel, or applies the reserve to the wrong leg.
Candidates memorize 'trip fuel plus reserve' as a phrase but do not build the fuel plan from the regulatory definitions; under time pressure they grab the first fuel number on the flight plan form and stop.
What to do instead
Before any fuel question, write the four components in order: taxi, trip, reserve (45 min or as specified), alternate, and any holding/contingency. Compute each from the given burn rate and time, then sum. Practice with three different aircraft burn rates until the sequence is automatic.
On an instrument approach chart, the candidate reads the MDA or DA correctly but then uses the wrong visibility or RVR value, or applies the approach minima for the wrong approach category.
Approach category is determined by Vref at maximum certificated landing weight, not by the actual approach speed flown; candidates also confuse straight-in minima with circling minima and pick the first line of the minima table.
What to do instead
For every approach question, first state the aircraft's approach category from its Vref, then locate the correct minima row (straight-in vs circling) and column (visibility vs RVR). Build a one-page table of categories A–D and drill ten chart excerpts until the lookup order is fixed.
When computing a holding pattern entry or the outbound heading, the candidate determines the entry type correctly but then applies the wrong wind correction or forgets to account for the inbound course when turning outbound.
Candidates treat the holding fix radial as the inbound course without converting it, and they apply a wind correction derived from the outbound leg instead of the inbound leg; the standard one-minute leg timing is also misapplied at altitude.
What to do instead
Use a fixed three-step routine: (1) convert the holding radial to the inbound course, (2) determine entry from the aircraft heading relative to the fix, (3) compute outbound heading with wind correction and adjust leg time for altitude. Practice with a wind triangle drawn for each of the three entry types.
The candidate calculates density altitude but then uses the wrong pressure altitude or temperature, or applies the result to the wrong performance chart (takeoff vs climb vs landing).
Pressure altitude is computed from altimeter setting and elevation, and candidates often use field elevation directly or use indicated altitude instead of pressure altitude; they also mix up the units (feet vs meters) and chart axes.
What to do instead
Standardize the calculation: pressure altitude = field elevation + (29.92 − altimeter setting) × 1000. Then find the density altitude from the chart using OAT. Keep a single flow: pressure altitude → temperature → density altitude → specific performance chart. Do five chart reads with different altimeter settings and temperatures until the axis labels are checked every time.
When interpreting a weather depiction, the candidate reads the surface analysis chart as if it were a forecast, or mistakes the freezing level for the icing layer and ignores the forecast valid time.
Charts use similar symbols and abbreviations; candidates skim the legend and do not check the valid time or the difference between observed and forecast products, especially under time pressure.
What to do instead
For every weather product, first state its type (observation vs forecast) and valid time, then read the legend before extracting values. Practice with paired surface analysis and prog chart excerpts, writing one sentence for each: what it shows, when it is valid, and what it implies for the flight.
The candidate plans a route using airway segments but fails to check minimum reception altitude (MRA), minimum enroute altitude (MEA), or changeover points, and then accepts a clearance that cannot be flown on the planned route.
Candidates focus on the route line on the chart and ignore the altitude and reception data printed along the airway; they also assume a direct route is always available without checking navigation aid coverage.
What to do instead
For each airway segment, read and record the MEA, MRA, and changeover point before accepting the route. Build a route log with one row per segment and fill in the four data items. Practice with three different low-altitude chart excerpts until the data extraction is routine.
When answering an IFR clearance or procedure question, the candidate confuses the clearance limit with the destination airport and does not apply the lost-communications or clearance-void-time rules correctly.
Clearance limits are often a fix short of the destination; candidates also memorize the lost-comm route without understanding the 'last assigned' and 'minimum altitude' rules, so they apply them out of order.
What to do instead
Write the lost-communication sequence as a numbered checklist: last assigned route, then minimum altitude, then direct to the clearance limit, then the published lost-comm route. For each practice clearance, underline the clearance limit and the void time before answering. Drill five clearances until the checklist is used every time.
The candidate computes weight and balance using the wrong datum or arm, or forgets to include the zero-fuel weight and landing weight limits in addition to takeoff weight.
Candidates memorize a single moment equation and apply it to every problem, but different aircraft use different datum conventions and some problems require checking both takeoff and landing limits; the zero-fuel weight is often omitted.
What to do instead
For each problem, list all four limits to check: maximum takeoff weight, maximum landing weight, maximum zero-fuel weight, and center of gravity range. Compute moments from the stated datum and convert units carefully. Practice with two aircraft types that use different datum conventions until the four-limit check is automatic.
When interpreting an icing or turbulence forecast, the candidate uses the forecast severity as if it were an observation and does not adjust the flight plan for the forecast freezing level or the turbulence layer.
Forecasts are probabilistic and time-bounded; candidates treat the worst-case value as certain and either over-plan or ignore it, and they do not cross-check the freezing level against the planned altitude.
What to do instead
For each forecast, state the valid time, the probability or severity, and the vertical extent. Then compare the planned altitude to the freezing level and turbulence layer and record one mitigation (altitude change, route change, or delay). Practice with three forecast excerpts and write the mitigation for each.
The candidate answers a radio navigation question by identifying the facility type but then misinterprets the course deviation indicator, the TO/FROM flag, or the CDI sensitivity for the segment being flown.
Candidates learn the instrument panel picture but not the geometry behind it; they forget that full-scale deflection corresponds to different widths on a localizer versus a VOR, and they misread the TO/FROM flag when the selected course is more than 90 degrees from the aircraft heading.
What to do instead
Draw the geometry for each question: aircraft position, selected course, and the resulting CDI deflection and flag. Memorize the full-scale deflection values (localizer and VOR) and the rule that the TO/FROM flag depends on the selected course, not the aircraft heading. Drill ten CDI excerpts with a sketch for each.