Keeping up with aviation apps for the iPhone is nearly a full-time job, but staying current on these app can definitely be worth it. A good example is the suite of reasonably-priced apps from CFI Tools. This suite consists of seven apps and each has the stated goal of doing one task and doing it well, rather than trying to be the aviation/iPhone equivalent of a Swiss Army Knife. The advantage of this approach is that you only need purchase the apps that you want or need. Let's take look at each of the apps in turn; The Crosswind Calculator, Holds Pattern Calculator, VOR Viewer, Weight & Balance, Mvx Tracks, Takeoff & Landing Distance, and Area Wx.
The $1.99 Crosswind Calculator lets you enter reported surface winds and the runway heading, then shows you the crosswind and headwind component along with a nice graphic. While there are tables and rules of thumb for calculating crosswind component, this low-cost app is easy to use. It's particularly attractive for student pilots who have crosswind component limitations on their solo endorsement.
Holding, Holding, Holding
The $2.99 Holds Calculator is a great learning tool for pilots working toward their instrument rating or for instrument pilots who need to brush off the rust and dust. Two slider controls let you set your aircraft's current heading and the holding course. The hold and recommended entry procedure are displayed two ways: One is superimposed over a heading indicator and the other is a north-up map-style view. A button lets you select standard (right turns) or non-standard (left) turns. I found the two sliders to be small enough that they were hard to get a hold of to move. This is not a big deal on the ground, but if you tried to use this app in a moving aircraft, well ...
When selecting the holding course with the slider, remember that this calculator wants you to enter the inbound course to the fix. I find this a little counter intuitive for a couple of reasons. First off, holding instructions include a cardinal direction and usually a radial and in most cases (except for station-side holds) these both represent the no-wind outbound heading. Secondly, when preparing to fly a hold the first step is to proceed to the holding fix and the second step is to turn outbound. With the Holds Calculator you can determine the inverse of the radial to get the inbound course by looking at the red line superimposed on the heading indicator. Maybe it's just me, but this seems a bit awkward.
Perhaps this could be made a bit less confusing by labeling the slider as Inbound Crs and by automatically calculating and displaying the outbound course as a number somewhere. Or perhaps there could be an option that would allow you to specify whether you want the slider to show the outbound course or the inbound course. Even with these shortcomings, the calculator is a good learning tool since it helps pilots learn how to visualize their holding course on a heading indicator or CDI.
The $3.99 VOR Viewer is a good learning tool for student pilots who are trying to get their head around VOR navigation. You set the aircraft's heading and the desired course with separate sliders. There's a separate button for aircraft control with three settings: Gravity, Random, and Drag. On the left side, the viewer gives you a plan view of the aircraft, the VOR station, and the selected course as a red line. On the right, you see a horizontal situation indicator with a course deviation bar, a to/from indicator and the current heading. Pretty cool and even though many training aircraft don't have an HSI, it's a good teaching and learning tool.
Weight & Balance
With the $5.99 Weight and Balance tool there's no reason to ever fly over gross weight or outside the allowable CG range. Several templates are provided for many popular GA aircraft or you can create your own. There's no template for the C172S model and given how popular this aircraft type is, it seems reasonable to expect the tool should include that aircraft. It would also be cool if the templates for popular aircraft were displayed separately from the fleet of aircraft that the user can create. This is probably not a big deal for folks who only fly one aircraft.
Tap the Update button to change the aircraft's weight, usable fuel and taxi fuel data.
Tap the Stations button to change the weight of passengers, baggage, and fuel on board. The two plotted weight/CG points represent the takeoff weight and loaded zero-fuel weight.
Tap the Envelope button to define the aircraft's weight and moment limits so they can be graphed. Perhaps there's a way to define a zero fuel limit and to define two separate envelopes (such as normal and utility), but I haven't yet figured that out.
The stated purpose of this $7.99 application is to save ground tracks from your flights so you can analyze flight maneuvers, but to do this your iPhone cannot be in airplane mode or the built-in GPS will be disabled. Not having your iPhone in airplane mode is a violation of 47 CFR 22.295 so I haven't tried this app. Remember that the FAA doesn't care if you leave your phone on during flight as long as you've determined that it doesn't interfere with navigation or communication. The FCC does care and prohibits a cell phone being on during flight, yet many iPhone aviation apps depend on the phone not being in airplane mode. What's up with that anyway?
Takeoff and Landing Performance
For $4.99 this tool provides you with takeoff and landing data for nine popular GA aircraft. You can enter the field conditions or, if you have network connectivity, the tool will automatically retrieve the METAR. The tool calculates the pressure altitude, you enter your aircraft's weight, and you'll see a display of the takeoff and landing performance for all available runways. The options page lets you specify your desired units of measure for temperature, wind speed, distance, and weight. Pretty cool!
The newest addition to the CFI Tools stable is the $6.99 AreaWX app that displays a list of surface observations for airports within a specified radius of a particular airport. You can tell the app you want to start with a map view or a list of station METARs.
The map view lists the METAR for each station in a color-coded box that quickly tells you whether that airport is VFR, MVFR, IFR or Low IFR. You can zoom the map using the usual iPhone gestures.
Tap on a station report in the station list and you'll see the full METAR and TAF for that airport. There's even a button that gives you the option of translating the METAR and TAF.
All in all, CFI Tools provides a significant amount of bang for not a lot of bucks. You get to choose which tools you want without having to commit to a big package and each tool does a single, well-defined task and generally does it well. Check it out!