General Quest Flashcards
(249 cards)
1
Q
What is the definition of Performance in aviation?
A
Ability of an aircraft at any stage of flight in terms of altitude, speed, weight, distance, and climb gradient
2
Q
What are the types of Performance?
A
- Mandatory Performance
- Gross Performance
- Net Performance
3
Q
What is Mandatory Performance?
A
Performance required for certification
4
Q
What is Gross Performance?
A
Average performance of a fleet of aircraft
5
Q
What is Net Performance?
A
Performance after considering aircraft aging, runway condition, and maintenance
6
Q
True or False: Net Performance is greater than Gross Performance.
A
False
7
Q
What does TORA stand for?
A
Takeoff Run Available
8
Q
What is defined as a rectangular area used for takeoff and landing?
A
Runway
9
Q
What is a Stopway?
A
Area beyond the runway used to stop aircraft during aborted takeoff
10
Q
What is a Clearway?
A
Rectangular area on ground/water that allows initial climb to a screen height
11
Q
What is the screen height for Class A jets?
A
35 ft
12
Q
What is the maximum length of a Clearway?
A
Cannot exceed half the runway length
13
Q
What is the width of a Clearway?
A
75 m or 250 ft either side of centerline (total 500 ft or 125 m)
14
Q
What is the slope requirement for a Clearway?
A
Should not project above a plane sloping at 1.25% upward from end of runway
15
Q
What does ASDA stand for?
A
Accelerate Stop Distance Available
16
Q
How is ASDA calculated?
A
TORA + Stopway
17
Q
What does TODA stand for?
A
Takeoff Distance Available
18
Q
How is TODA calculated?
A
TORA + Clearway
19
Q
What does LDA stand for?
A
Landing Distance Available
20
Q
How is LDA calculated?
A
Runway length (THD to THD)
21
Q
What does IAS stand for?
A
Indicated Airspeed
22
Q
What does CAS/RAS stand for?
A
Calibrated / Rectified Airspeed
23
Q
What is Equivalent Airspeed (EAS)?
A
CAS corrected for compressibility
24
Q
What is True Airspeed (TAS)?
A
EAS corrected for air density
25
What does GS stand for?
Ground Speed
26
True or False: All V-speeds are based on CAS.
True
27
What is VMCG?
Minimum Controllable Speed on Ground
28
What is the definition of VMCG?
Minimum CAS during takeoff run where if one engine fails, the aircraft can still maintain directional control and continue takeoff safely
29
What are the conditions for VMCG?
* Using rudder only
* Pedal force not exceeding 150 pounds
* Assume 7 knots crosswind from the inoperative engine side
* No thrust reduction on operative engine
30
What is the relationship between V1 and VMCG?
V1 ≥ VMCG
31
What is the relationship between V1 and VR?
V1 ≤ VR
32
What is the relationship between V1 and VMBE?
V1 ≤ VMBE
33
What is the formula for Calibrated Airspeed (CAS)?
CAS = √(2 × q / ρ) or q = ½ × ρ × V²
34
What does q represent in the CAS formula?
Dynamic pressure
35
What does ρ (rho) represent in the CAS formula?
Air density
36
What does V represent in the CAS formula?
True Airspeed (TAS)
37
What is the lift formula?
Lift = ½ × ρ × V² × CL × S
38
What does CL represent in the lift formula?
Coefficient of Lift (based on angle of attack)
39
What does S represent in the lift formula?
Wing Surface Area
40
How does lift change with True Airspeed (TAS)?
Lift ∝ TAS²
41
What happens to lift if TAS doubles?
Lift increases 4×
42
What happens to lift if TAS triples?
Lift increases 9×
43
What can be done to increase lift?
* Increasing TAS
* Increasing angle of attack (CL)
44
What is the weight of the aircraft when stationary on the runway?
100 units
45
What happens when brakes are released and thrust is applied?
* Thrust (T) acts forward
* Drag (D) opposes motion
* Lift (L) begins generating as speed increases
46
At what point does an aircraft lift off?
When Lift ≥ Weight
47
What are the stages of forces acting on the aircraft during takeoff?
* Start: Weight 100, Thrust Applied, Drag Begins 0–20
* Mid-Runway: Weight 100, More Thrust, More Drag ~50
* Lift-Off Point: Weight 100, High Thrust, High Drag 100+
48
What is the definition of VSO?
Stalling Speed in Landing Configuration
49
What is the definition of VS1?
Stalling Speed in Takeoff/Clean Configuration
50
What is the typical stalling speed (VSO) for small aircraft?
~40 knots
51
What is the typical stalling speed (VS1) for small aircraft?
~50 knots
52
True or False: All aeroplanes are aircraft.
True
53
True or False: All aircraft are aeroplanes.
False
54
What is the difference between Aircraft and Aeroplane?
Aircraft includes helicopters, gliders, UAVs, etc. Aeroplanes are fixed-wing aircraft.
55
What is the minimum speed for directional control on ground in case of engine failure?
VMCG
56
What is the minimum airspeed for directional control in air after engine failure?
VMCA
57
What does VEF stand for?
Engine Failure Speed
58
What is the V1 (Decision Speed)?
Speed by which the pilot must decide whether to continue or abort takeoff
59
What happens if an engine fails before V1?
Abort takeoff (sufficient ASDA to stop)
60
What happens if an engine fails after V1?
Continue takeoff (not enough ASDA to stop safely)
61
What factors affect V1?
* Aircraft weight
* Runway length
* Temperature
* Air density
* Runway surface (wet/dry/contaminated)
* Available stopway (ASDA)
62
What is the minimum safe speed to be achieved at screen height?
V2 (Takeoff Safety Speed)
63
What is the screen height requirement for safe takeoff?
Minimum 35 feet (can be higher, but not lower)
64
What is the relationship between VR and V1?
VR ≥ V1
65
What is the relationship between V2 and VLOF?
V2 ≥ 1.1 × VLOF
66
What is the relationship between V2 and VS?
V2 ≥ 1.2 × VS
67
What is the typical stalling speed for small aircraft?
14–15 knots
68
What are the conditions for VMCG?
* Use of rudder only
* Rudder pedal force ≤ 150 lbs
* Assume 7 knots crosswind from inoperative engine side
* No thrust reduction on the live engine
69
What are the two configurations considered for stalling speeds?
* VSO (Dirty Configuration)
* VS1 (Clean Configuration)
70
What is the configuration for VSO?
Landing configuration (gear extended, flaps deployed)
71
What is the configuration for VS1?
Takeoff/Clean configuration (gear retracted, flaps up or set to takeoff position)
72
What is the meaning of VSO?
Stalling speed in landing configuration
## Footnote
VSO is approximately 40 knots for a Cessna 152.
73
What is the meaning of VS1?
Stalling speed in take-off configuration
## Footnote
VS1 is approximately 50 knots for a Cessna 152.
74
What characterizes a Dirty Configuration?
Landing gear extended/down, flaps and slats deployed
75
What characterizes a Clean Configuration?
Landing gear retracted/up, flaps/slats retracted
76
Why is VS1 considered more dangerous than VSO?
It provides less margin from cruise speed, increasing stall risk.
77
Define VMCA.
Minimum control speed in air, the minimum airspeed to maintain directional control after engine failure.
78
What are the worst-case assumptions for VMCA?
* Use of rudder only
* Rudder pedal force ≤ 150 lbs
* Bank angle ≤ 5°
* Directional deviation ≤ 20°
* No reduction in thrust on the live engine
* Negligible ground effect
79
What is Ground Effect?
Cushioning of air between the aircraft and the runway caused by disrupted wingtip vortices near the ground.
80
What is VEF?
Engine Failure Speed, the assumed speed at which engine failure is calculated for performance planning.
81
What is V1?
Decision speed, the maximum speed at which the pilot must decide to abort or continue takeoff.
82
What happens if engine failure occurs before V1?
Pilot must abort takeoff.
83
What happens if engine failure occurs at or after V1?
Pilot must continue takeoff.
84
What is the consequence of aborting takeoff after V1?
Aircraft may overrun the runway.
85
What is VMBE?
Maximum brake energy speed, the maximum speed at which full brake application will not adversely affect the brake system.
86
What is VR?
Rotation speed, the speed at which the pilot initiates aircraft rotation.
87
What is VMU?
Minimum unstick speed, the theoretical minimum speed at which the aircraft can become airborne.
88
What is VLOF?
Lift-off speed, the actual speed at which the aircraft leaves the ground after rotation.
89
What does V2 represent?
Take-off safety speed, the CAS that must be achieved at 35 feet AGL within the clearway.
90
What is the significance of V1 ≥ VMCG?
V1 must be greater than or equal to Minimum Control Speed on Ground.
91
What is the maximum allowable runway slope?
±2 degrees, unless topographic conditions demand otherwise.
92
What effect does a wet runway have on performance?
Reduced braking, slight hydroplaning risk, lower V1 than dry.
93
What is hydroplaning?
A dangerous condition where aircraft tires lose contact with the runway surface due to a thin layer of water.
94
What is the formula for hydroplaning speed?
Hydroplaning Speed (knots) = 9 × √(Tire Pressure in PSI)
95
What is the service ceiling?
Maximum altitude at which Rate of Climb = 100 ft/min.
96
What is the absolute ceiling?
Maximum altitude where Rate of Climb = 0 ft/min.
97
Define Center of Gravity (CG).
The point through which the force of gravity acts on an aircraft's mass.
98
What is a Datum in aircraft context?
A reference point on the aircraft's longitudinal axis for weight and balance calculations.
99
What is the formula for Moment?
Moment = Mass × Arm.
100
What happens to stall speed (VS) with a FORE CG?
Increases.
101
What happens to stall speed (VS) with an Aft CG?
Decreases.
102
What does BEM stand for?
Basic Empty Mass, the mass of the aircraft as received from the manufacturer.
103
What is Dry Operating Mass (DOM)?
Includes BEM, crew, baggage, catering, and potable water.
104
What is Payload in aviation terms?
Revenue-generating load (passengers, baggage, cargo).
105
What does DOM stand for?
Dry Operating Mass
## Footnote
Also referred to as BOM (Basic Operating Mass) and APS (Aircraft Prepared for Service).
106
What is included in the Dry Operating Mass (DOM)?
* BEM (Basic Empty Mass)
* Crew and crew baggage
* Catering and removable passenger service equipment
* Potable water and lavatory chemicals
* Food and beverages
107
Define Payload in the context of aviation.
Revenue-generating load (passengers, baggage, cargo)
108
What is Traffic Load?
Payload plus certain non-revenue-generating loads
109
What does FOB stand for?
Fuel On Board (Total Fuel)
## Footnote
Includes trip fuel, contingency fuel, alternate fuel, reserve fuel, and holding fuel.
110
What is the formula for Useful Load?
Payload + Usable Fuel
111
How is Operating Mass (OM) calculated?
OM = DOM + Takeoff Fuel
112
What does ZFM stand for?
Zero Fuel Mass
113
What does TOM represent?
Takeoff Mass
114
What is the formula for Landing Mass (LM)?
LM = TOM – Trip Fuel
115
How is Ramp Mass (RM) calculated?
RM = DOM + Taxi & Startup Fuel
116
What is Ballast Fuel used for?
To keep CG (Center of Gravity) within limits
117
What is the Max Structural Takeoff Mass (MS TOM)?
Max permissible takeoff mass set by manufacturer
118
Define Performance Limited Takeoff Mass (PL TOM).
Max takeoff mass limited by current aerodrome conditions
119
What does R TOM / M TOM stand for?
Regulated or Maximum Takeoff Mass
120
What is the approach for mass calculation in exams?
* Create a table of values
* Choose the lowest value among M TOM, MLM + Trip Fuel, MZFM + Takeoff Fuel
121
What does AUM stand for?
All-Up Mass = Takeoff Mass (TOM)
122
How is a Flight Plan defined?
Initial flight plan created on ground to inform ATS about the intended flight
123
What is a Filed Flight Plan (FPL)?
PLN submitted to ATS/ATC by the pilot or designated representative
124
What is a Current Flight Plan (CPL)?
Revised version of FPL if changes are made
125
What is a Repetitive Flight Plan (RPL)?
For regularly recurring flights filed once and retained by ATS for reuse
126
What is the validity period of a Flight Plan?
Valid from -15 minutes to +45 minutes of EOBT
127
What are the flight rules indicated in Box 8 of a flight plan?
* I: IFR
* V: VFR
* Y: IFR → VFR
* Z: VFR → IFR
128
What does Box 9 of a flight plan detail?
Aircraft details including number of aircraft and type of aircraft
129
What equipment codes are included in Box 10 of a flight plan?
* D – DME
* F – ADF
* G – GNSS
* H – HF RTF
* L – ILS
* N – No COM/NAV aid
* O – VOR
* V – VHF RTF
130
What is the formula for Distance to CP (Critical Point)?
DCP = (D × H) / (O + H)
131
Define Point of No Return (PNR).
Farthest point on your route from which you can return to departure aerodrome within safe fuel endurance
132
What is the formula for Distance to PNR (DPNR)?
DPNR = (E × O × H) / (O + H)
133
What does the term Convergence refer to in navigation?
Angle of inclination between two meridians at a given latitude
134
What is the Compression Ratio of the Earth?
1 / 297 ≈ 0.3%
135
What does the 1 in 60 Rule state?
If an aircraft is 1 NM off track after flying 60 NM, it has a track error of 1°
136
What is the formula for Track Error (TE)?
TE = (60 × Off Track Distance) ÷ Distance Covered
137
What shape is the Earth described as?
Oblate Spheroid
138
What is the compression of the Earth?
0.3%
## Footnote
Compression Ratio = 1 / 297 ≈ 1 / 300
139
What are the equatorial and polar diameters of the Earth?
Equatorial Diameter: 6880 NM; Polar Diameter: 6857 NM
140
What is the difference in diameter between the equator and the poles?
23 NM (≈ 277 statute miles or 43 km)
141
What is the formula for calculating compression?
Compression = (Major Axis − Minor Axis) ÷ Major Axis
142
What is the relationship between nautical miles and kilometers?
1 NM = 1.852 km
143
What is Earth's circumference in nautical miles?
216,000 NM
144
How does the Earth rotate when viewed from the North Pole?
Anti-clockwise
145
How does the Earth rotate when viewed from the South Pole?
Clockwise
146
What are the latitude and longitude measurements for the equator?
Latitude: 0°; Longitude: not applicable
147
What are the important latitude circles?
* Equator – 0°
* Tropic of Cancer – 23.5° N
* Tropic of Capricorn – 23.5° S
* Arctic Circle – 66.5° N
* Antarctic Circle – 66.5° S
148
Define a Great Circle (GC).
Largest circle that can be drawn on Earth, shortest distance between two points
149
What is a Rhumb Line (RL)?
A line that cuts all meridians at the same angle
150
What is the difference between a Great Circle and a Rhumb Line in terms of distance?
Great Circle: Shortest path; Rhumb Line: Longer than GC
151
What is WGS-84?
World Geodetic System – 1984, standard model used for GPS and charts
152
What is the relationship between degrees, minutes, and seconds?
1 degree = 60 minutes; 1 minute = 60 seconds
153
What is the formula for calculating distance in nautical miles?
Distance (North–South) = ΔLatitude × 60
154
What is the formula for calculating departure in nautical miles?
Departure (East–West) = ΔLongitude × 60 × cos(latitude)
155
What does the antipodal concept refer to?
Points exactly opposite on Earth
156
How is distance calculated if the coordinates are not antipodal?
Use formulas: Distance (North-South) = ΔLatitude × 60; Departure (East-West) = ΔLongitude × 60 × cos(latitude)
157
What is an Isogonic Line?
Joins points of equal magnetic variation
158
Define True North.
Geographic North
159
What is Magnetic North?
Where magnetic needle aligns due to Earth’s magnetic field
160
What is Compass North?
Affected by aircraft’s internal interference (metal/electrical)
161
What is variation in navigation?
Angle between True North and Magnetic North
162
What is deviation in navigation?
Angle between Magnetic North and Compass North
163
What is track in aviation?
Path over the ground (can be True, Magnetic, or Compass)
164
What is heading in aviation?
Direction aircraft nose is pointing (True, Magnetic, Compass)
165
What is drift in aviation?
Angular difference between Track and Heading
166
How does wind affect True Air Speed (TAS) and Ground Speed (GS)?
Nil wind → TAS = GS; Headwind → TAS > GS; Tailwind → TAS < GS
167
What is the formula for calculating headwind?
Headwind = V × cos(θ)
168
What is Endurance in aviation?
Time aircraft can fly with available fuel
169
What is the formula for Total Endurance?
Total Endurance = FOB ÷ FC
170
What does the term 'Graticule' refer to?
A network of meridians (longitudes) and parallels (latitudes)
171
What is the difference between maps and charts?
* Maps: Show detailed geographical features
* Charts: Contain minimal geographical features, primarily for navigation
172
What is projection in cartography?
The process of transferring the Earth’s curved surface onto a flat surface
173
What are the ideal features of a map projection?
* Scale should be correct and constant
* Shape should be represented accurately
* Area should be preserved where required
* Bearings should match Earth’s
* Meridians and Parallels should intersect at 90°
174
What is Orthomorphism?
Bearings are correctly represented; achieved when meridians and parallels intersect at 90°
175
What are the types of projection?
* Perspective Projections
* Non-Perspective Projections
176
What is the Mercator Projection known for?
Best for rhumb line (RL) navigation; correct at equator but distorted at higher latitudes
177
What is Lambert’s Conformal Conic Projection best suited for?
Best for mid-latitude regions (10°–70° N/S)
178
What is the Polar Stereographic Projection ideal for?
Ideal for polar regions above 70° latitude
179
What is the Transverse Mercator Projection used for?
Suitable for areas with more north-south extent, like national topographic maps
180
What is the Oblique Mercator projection characterized by?
Correct along great circle of tangency; usable as constant scale within 500 NM
181
How does Lambert’s Conformal projection behave?
Correct at standard parallels; expands outside, contracts within; min at origin
182
What is the Transverse Mercator projection correct at?
Correct at datum meridian; expands away as secant of great circle distance
183
What is the convergence behavior of the Mercator projection?
Correct at equator; less than Earth convergence elsewhere
184
In Polar Stereographic projection, what does chart convergence equal?
Change in longitude
185
How does the Lambert’s Conformal projection define convergence?
Convergence = Δlongitude × sin(parallel of origin)
186
What is the rhumb line behavior of the Mercator projection?
Straight line
187
How do great circles behave in the Mercator projection?
Curves convex to nearer pole and concave to equator
188
What is the definition of magnetic dip?
The angle between the horizontal plane and the axis of a freely suspended magnetic needle
189
What are the two components of Earth’s magnetic field?
* Horizontal Component (H)
* Vertical Component (Z)
190
What is the formula for the Horizontal Component (H)?
H = T × cosθ
191
At which latitude is the Horizontal Component (H) maximum?
Equator (θ = 0°)
192
What is the formula for the Vertical Component (Z)?
Z = T × sinθ
193
When is the Vertical Component (Z) maximum?
At the poles (θ = 90°)
194
What requirements ensure a good compass?
* Horizontality
* Sensitivity
* Aperiodicity
195
What properties should the liquid used in a magnetic compass have?
* Colorless
* Transparent
* High boiling point
* Low freezing point
* Low viscosity
* Low coefficient of expansion
* Non-corrosive
196
What is the Northern Hemisphere rule for turning errors?
UNOS: Under-read while turning through North → Undershoot; Over-read while turning through South → Overshoot
197
What does the acronym ANDS stand for in relation to compass errors?
Accelerate → apparent turn to North; Decelerate → apparent turn to South
198
What is the formula for total compass deviation?
Deviation = A + B × sin(heading) + C × cos(heading)
199
What is the definition of the Agonic Line?
Line joining places of zero magnetic variation
200
What is the difference between variation and deviation?
* Variation: Angle between True North and Magnetic North
* Deviation: Compass error caused by magnetic interference from aircraft components
201
What is Hard Iron Magnetism?
Permanent magnetism that is difficult to magnetize but retains magnetism permanently
202
What is Soft Iron Magnetism?
Temporary magnetism that is easily magnetized but loses magnetism when the magnetic force is removed
203
What are the components of a Direct Reading Magnetic Compass (DMRC)?
* Magnetic Needle
* Compass Card
* Damping Fluid
* Housing
204
What is the function of the damping fluid in a magnetic compass?
Reduces oscillations
205
What is the inclination of the Earth's axis?
23.5° from the perpendicular to its orbital plane
206
What does the declination of the Sun vary between?
+23.5° (North) to -23.5° (South)
207
What is the significance of the Tropic of Cancer and Tropic of Capricorn?
Sun is overhead twice a year between these latitudes
208
What is Kepler’s First Law?
Planets move in elliptical orbits with the Sun at one focus
209
What is the duration of a Sidereal Day?
23 hours 56 minutes 4 seconds
210
What is the definition of static margin in aircraft balance?
Distance between the neutral point and aft CG limit
211
What is the World Geodetic System 1984 (WGS84)?
Standard model used for geodesy and GPS
212
What causes the Earth's rotation?
Causes day and night
213
What causes the revolution of the Earth?
Causes 1 year
214
What is the definition of apparent solar day?
Time from one noon to next based on real Sun
215
How does the compass behave when turning through North in the Northern Hemisphere?
Underreads / lags
216
What happens to the compass during acceleration on an easterly heading in the Northern Hemisphere?
Apparent turn towards North
217
What is the maximum difference between Geodetic latitude and Geocentric latitude?
11.6 minutes at 45° N/S
218
What is the duration of a Sidereal Day?
23 hours 56 minutes 4 seconds
## Footnote
A Sidereal Day is the time it takes for Earth to complete one full rotation (360°) with respect to a distant star.
219
What defines an Apparent Solar Day?
Time from one noon to next based on real Sun
## Footnote
The duration varies due to Earth's elliptical orbit.
220
What are the durations of the Apparent Solar Day in November and February?
* 23 hr 44 min in November
* 24 hr 14 min in February
221
What is a Mean Solar Day?
Based on an imaginary mean Sun moving uniformly in a circular orbit
## Footnote
Duration = 24 hours.
222
What is the maximum difference between Mean and Apparent Solar Day in November and February?
* November: 16 minutes
* February: 14 minutes
223
Define Local Mean Time (LMT).
Measured from mean Sun, differs by longitude
224
What is the definition of a Sidereal Year?
Time Earth takes to return to same point relative to a star
## Footnote
Duration = 365 days 6 hours 9 minutes.
225
What is a Tropical Year?
Time Earth takes to return to same point and orientation relative to the Sun
## Footnote
Duration = 365 days 5 hours 49 minutes.
226
How is a Calendar Year defined?
Defined as 365 days to closely match the tropical year
227
What is a leap year?
A year with 366 days, added every 4th year to compensate for the shortfall
228
What is Zenith?
The point directly overhead the observer on the celestial sphere
229
Define Nadir.
The point on the celestial sphere diametrically opposite to the zenith
230
What is the Celestial Horizon?
An imaginary plane that passes through the Earth’s center and is perpendicular to the zenith–nadir line
231
What is the Sensible Horizon?
The plane parallel to the celestial horizon, passing through the observer’s eye level
232
What does the Visible Horizon represent?
The circle bounding the observer’s view of the Earth’s surface under clear atmospheric conditions
233
What is Twilight?
The period before sunrise and after sunset when there is still natural light in the atmosphere
234
What is Civil Twilight?
Occurs when the Sun’s center is between 0° and 6° below the sensible horizon
235
Define Nautical Twilight.
Occurs when the Sun’s center is between 6° and 12° below the sensible horizon
236
What is Astronomical Twilight?
Occurs when the Sun’s center is between 12° and 18° below the sensible horizon
237
What are the dates of the Equinoxes?
* 21st March – Spring (Vernal) Equinox
* 21st September – Autumnal Equinox
238
What happens during the Summer Solstice in the Northern Hemisphere?
* Date: 21st June
* Sun’s Declination: 23.5° North
* Longest Daylight Duration
239
What occurs during the Winter Solstice in the Northern Hemisphere?
* Date: 22nd December
* Sun’s Declination: 23.5° South
* Shortest Daylight Duration
240
What is GMT?
Greenwich Mean Time
241
What is UTC?
Coordinated Universal Time
242
What is Zulu Time?
UTC expressed in aviation using the letter Z
243
What is the relationship between longitude and time?
* East Longitude → Time Increases
* West Longitude → Time Decreases
244
What is a Meridian?
A line of constant longitude
245
Define Local Mean Time (LMT) in relation to the Mean Sun.
When the Mean Sun crosses a meridian, LMT is 1200 hours; at the anti-meridian, LMT is 0000 hours
246
What is Standard Time?
A fixed time set by a country’s authorities for uniformity
247
What is the International Date Line (IDL)?
A zigzag line near the 180° meridian, avoiding populated areas
248
What happens when crossing the IDL eastward?
Subtract 1 day → Repeat the date
249
What happens when crossing the IDL westward?
Add 1 day → Skip a date
