A method and device for identifying and analyzing pilot landing ability

Abstract

The present invention provides a method and device for identifying and analyzing a pilot's landing ability, and belongs to the field of aviation safety and safety management. The method comprises: obtaining flight data before the aircraft lands; processing the pitch rate in the flight data by a pitch rate sequence change point detection algorithm to obtain the peaks and troughs of the pitch rate; and determining the dynamic behavior of the aircraft when approaching the ground according to the peaks and troughs of the pitch rate. The present invention proposes for the first time a pilot landing ability identification system based on a combination of change point detection and pattern recognition with data drive, which has broad application prospects and significant practical value.

Description

Technical Field

[0001] The invention belongs to the field of aviation safety and safety management, and in particular relates to a pilot landing ability identification and analysis method and system. Background Art

[0002] As an important part of modern transportation, civil aviation has always attracted worldwide attention for its efficiency and speed. With the continuous development and progress of the industry, the accurate analysis and management of flight data has become the cornerstone of decision-making to ensure flight safety. In recent years, the use of Quick Access Recorder (QAR) data has been valued by airlines. It records various flight data of the aircraft in detail, allowing airlines to monitor the aircraft. The parameters in the QAR include but are not limited to the aircraft's altitude, speed, acceleration, attitude, as well as the pilot's operation details and the aircraft's immediate response to these operations.

[0003] In order to further improve the utilization value of QAR data, many technology companies have launched a variety of flight data analysis tools. Among them, "AeroMonitor" is popular among airlines for its in-depth mechanical failure and critical event analysis functions, which can help airlines identify potential aircraft hazards at the first time and take corresponding preventive measures; while "SkySight" stands out for its precise analysis of pilot operations, providing airlines with analysis of pilot operational errors, thereby providing more targeted training and guidance.

[0004] In recent years, with the advancement of technology and the sharp increase in flight data, flight data analysis tools on the market have also shown a flourishing trend. For example, advanced tools such as "FlightGuardian" and "AirSight" have demonstrated strong capabilities in big data processing, flight performance monitoring, and risk positioning. However, among these tools, there are only a few technologies and patents that can truly deeply identify the pilot's operating mode during the landing phase. Many tools may be able to provide us with general data analysis, but when faced with the specific behavior patterns of aircraft in critical flight phases, such as landing, these tools may seem powerless. For example, in many tools, the pitch rate pattern during flight may be ignored or not given enough attention, which undoubtedly increases flight risks.

[0005] In short, although existing technologies have performed well in processing flight big data and analysis, in order to truly grasp the behavioral patterns of pilots' operations during the landing phase, a more advanced, detailed and professional technical solution is urgently needed. Summary of the invention

[0006] Based on this, it is necessary to propose a method and device for identifying and analyzing pilot landing ability in response to the above problems.

[0007] The present invention is achieved through the following technical solutions:

[0008] A first aspect of the present invention provides a method for identifying and analyzing a pilot's landing ability, the method comprising:

[0009] Obtain flight data before the aircraft lands;

[0010] Processing the pitch rate in the flight data by using a pitch rate sequence change point detection algorithm to obtain peaks and troughs of the pitch rate;

[0011] The dynamic behavior of the aircraft when approaching the ground is determined based on the peaks and troughs of the pitch rate.

[0012] A further improvement of the present invention is:

[0013] The obtaining of flight data before the aircraft lands specifically includes:

[0014] Retrieve flight data from Quick Access Recorder (QAR) data;

[0015] The flight data includes pre-landing data, time data, ground distance, touchdown distance data, vertical load data VRTG, speed data, pitch rate, radio altitude, and time series data of attitude angle.

[0016] A further improvement of the present invention is:

[0017] The processing of the flight data by using a pitch rate sequence change point detection algorithm to obtain the peaks and troughs of the pitch rate specifically includes:

[0018] Select a window of size w and detect change points by sliding the window;

[0019] Determine the statistical characteristics within the window, and for each time point t, determine the mean of the pitch rate of the two windows [tw,t] and [t,t+w] and

[0020] Determine the loss value at this time point t through the loss function;

[0021] Determine whether a change point occurs at the time point t based on the comparison relationship between the loss value at the time point t and the threshold τ;

[0022] If it is determined that a change point occurs at the time point t, the peak or trough of the pitch rate is determined.

[0023] A further improvement of the present invention is:

[0024] Determining the loss value at the time point t by using the loss function specifically includes: Determine the loss value at this time point t.

[0025] A further improvement of the present invention is:

[0026] Determining the dynamic behavior of the aircraft when approaching the ground according to the peaks and troughs of the pitch rate specifically includes:

[0027] Determine the height and pitch rate (a1, b1) corresponding to adjacent wave crests, and the height and pitch rate (a2, b2) corresponding to wave troughs;

[0028] Determine a pitch rate slope Slope according to the height and pitch rate (a1, b1) corresponding to the adjacent wave crests and the height and pitch rate (a2, b2) corresponding to the wave troughs;

[0029] The comparison relationship between the absolute value corresponding to the pitch rate slope Slope and a given threshold determines the dynamic behavior of the aircraft when approaching the ground;

[0030] or,

[0031] Determining the dynamic behavior of the aircraft when approaching the ground according to the peaks and troughs of the pitch rate specifically includes:

[0032] Determine the height and pitch rate (a1, b1) corresponding to adjacent wave crests, and the height and pitch rate (a2, b2) corresponding to wave troughs;

[0033] Determine a pitch rate slope Slope according to the height and pitch rate (a2, b2) corresponding to the adjacent troughs and the height and pitch rate (a1, b1) corresponding to the peaks;

[0034] The comparison relationship between the absolute value corresponding to the pitch rate slope Slope and a given threshold value determines the dynamic behavior of the aircraft when approaching the ground.

[0035] A further improvement of the present invention is:

[0036] The comparison relationship between the absolute value corresponding to the pitch rate slope Slope and a given threshold determines the dynamic behavior of the aircraft when approaching the ground, specifically including: if the absolute value corresponding to the pitch rate slope Slope is greater than the given threshold, determining that the dynamic behavior of the aircraft when approaching the ground is a high slope change mode or a gradual slope change mode.

[0037] A further improvement of the present invention is:

[0038] Determining the dynamic behavior of the aircraft when approaching the ground according to the peaks and troughs of the pitch rate specifically includes:

[0039] determining at least one altitude interval range;

[0040] Set trough threshold and peak threshold;

[0041] According to whether there is a point in the pitch rate that satisfies a trough threshold and a peak threshold within the at least one altitude interval, the dynamic behavior of the aircraft when approaching the ground is determined according to the result.

[0042] A further improvement of the present invention is:

[0043] The determining, according to the pitch rate, whether there is a point that satisfies a trough threshold and a peak threshold within the at least one altitude interval, and determining the dynamic behavior of the aircraft when approaching the ground according to the result specifically includes:

[0044] If there is a point in the pitch rate that satisfies a trough threshold and a peak threshold within the at least one altitude interval, it is determined according to the result that the dynamic behavior of the aircraft when approaching the ground is a specific altitude range mode or a multi-level altitude change mode.

[0045] A further improvement of the present invention is:

[0046] The method further includes: determining a dynamic behavior of the aircraft as it approaches the ground based on the peaks, troughs, and remaining data in the flight data of the pitch rate;

[0047] Specifically, it includes: no peak or trough appears within the trough threshold and the peak threshold, and the distance to touchdown value (VRTG) is within an appropriate range to determine the dynamic behavior of the aircraft when approaching the ground and the stability mode before and after touchdown;

[0048] Alternatively, if the absolute value corresponding to the pitch rate slope Slope is less than or equal to a given threshold range, and the touchdown attitude or VERF-touchdown speed is less than a set threshold, it is determined that the dynamic behavior of the aircraft when approaching the ground is a touchdown micro-stability mode.

[0049] A second aspect of the present invention provides a device for identifying and analyzing a pilot's landing ability, the device comprising: a data acquisition unit, a pitch rate determination unit, and a behavior determination unit;

[0050] The data acquisition unit is used to acquire flight data before the aircraft lands;

[0051] The pitch rate determination unit is used to process the pitch rate in the flight data by using a pitch rate sequence change point detection algorithm to obtain a peak and a trough of the pitch rate;

[0052] The behavior determination unit is used to determine the dynamic behavior of the aircraft when approaching the ground according to the peaks and troughs of the pitch rate.

[0053] The embodiments of the present invention have the following beneficial effects:

[0054] The present invention proposes for the first time a pilot landing ability identification system based on the combination of change point detection and pattern recognition with data drive, which has broad application prospects and significant practical value. BRIEF DESCRIPTION OF THE DRAWINGS

[0055] Figure 1 A flowchart of a method for identifying and analyzing a pilot's landing ability is provided for an embodiment of the present invention;

[0056] Figure 2 A data graph of a high slope change mode in a method for identifying and analyzing a pilot's landing ability is provided for an embodiment of the present invention;

[0057] Figure 3 A data graph of a progressive slope change pattern in a method for identifying and analyzing a pilot's landing ability is provided for an embodiment of the present invention;

[0058] Figure 4 A data graph of a specific altitude range mode in a method for identifying and analyzing a pilot's landing ability is provided for an embodiment of the present invention;

[0059] Figure 5 A data diagram of a multi-level altitude change pattern in a method for identifying and analyzing a pilot's landing ability is provided for an embodiment of the present invention. DETAILED DESCRIPTION

[0060] The present invention is further described in detail below in conjunction with the accompanying drawings:

[0061] With the development of civil aviation, safety has become the focus of the industry and the public. Ensuring that every flight is safe, stable and efficient is the primary goal of every airline and pilot. In order to meet this demand, it is particularly important to analyze, understand and improve flight data during critical flight stages such as landing. Therefore, accurate identification and analysis of pilots' behavior patterns during the landing phase has a decisive impact on flight safety.

[0062] The embodiment of the present invention provides a method for identifying and analyzing a pilot's landing ability, such as Figure 1 As shown, the method includes:

[0063] Step 101: Acquire flight data before the aircraft lands;

[0064] Specifically, flight data is obtained from the Quick Access Recorder (QAR) data;

[0065] The flight data includes pre-landing data, time data, ground distance, touchdown distance data, vertical load data VRTG, speed data, pitch rate, radio altitude, and time series data of attitude angle.

[0066] Time Data: Timestamps are fundamental to each record, helping to align and synchronize various flight parameters and ensure data continuity and consistency.

[0067] Touchdown distance data: A key parameter that measures how far the aircraft is from the ground. It helps understand the aircraft's altitude changes during landing and determine whether the aircraft has touched the ground.

[0068] Vertical load data VRTG: This is a parameter that measures the vertical acceleration of the aircraft during landing. It can help understand the structural load of the aircraft and thus assess whether the aircraft has a hard landing. VRTG (Vertical Load Rating) is the vertical load rating experienced by the aircraft landing gear during landing. It usually refers to the maximum vertical load applied to the landing gear by the aircraft during landing, and is often measured in g (the acceleration of gravity of the earth).

[0069] Speed ​​data: Speed ​​data shows the speed change of the aircraft during landing. It is a key parameter for evaluating the aircraft landing performance and the pilot's operating skills.

[0070] The above data are directly decoded by the QAR decoding software. As features, such as vertical load, correspond to the VRTG column, it is time series data.

[0071] Furthermore, the flight data also includes flight attributes. In order to better analyze and compare the data of each flight, it is also necessary to record the unique attributes of each flight. For example: Flight number: a unique identifier for each flight, which helps to distinguish different flight missions. Other attributes: including aircraft type, flight date, etc.

[0072] Identify and differentiate flights by flight attributes to facilitate comparison of different flights.

[0073] Step 102: Processing the pitch rate in the flight data by using a pitch rate sequence change point detection algorithm to obtain peaks and troughs of the pitch rate;

[0074] Specifically, a window of size w is selected and the change points are detected by sliding the window;

[0075] Determine the statistical characteristics within the window, and for each time point t, determine the mean of the pitch rate of the two windows [tw,t] and [t,t+w] and

[0076] Determine the loss value at this time point t through the loss function;

[0077] Determine whether a change point occurs at the time point t based on the comparison relationship between the loss value at the time point t and the threshold τ;

[0078] If it is determined that a change point occurs at the time point t, the peak or trough of the pitch rate is determined.

[0079] Exemplarily, the threshold τ is a positive number, for example, τ=0.5. If L(t)≥0.5 is satisfied, the time point is considered to be a change point.

[0080] Afterwards, the average pitch rate at the time point t[t-3, t+3] is determined. If the average is greater than the pitch rate at the time point t, it is confirmed as a trough, otherwise it is a peak.

[0081] Step 103: Determine the dynamic behavior of the aircraft when approaching the ground according to the peaks and troughs of the pitch rate.

[0082] Specifically, in the civil aviation field, the pitch rate of an aircraft is a key parameter that reflects the stability and maneuverability of the aircraft in the vertical direction; for safety incidents occurring during the landing phase, the pitch rate may change significantly before and after landing; therefore, by monitoring these change points, potential risks can be identified and predicted in a timely manner.

[0083] The pitch rate sequence change point detection algorithm adopted in the present invention adopts a window-based method: this method detects change points by sliding a fixed-size window. When the data in the window has a significant difference with the data before and after it, the data in the window is regarded as a change point.

[0084] Determining the dynamic behavior of the aircraft when approaching the ground according to the peaks and troughs of the pitch rate specifically includes:

[0085] Determine the height and pitch rate (a1, b1) corresponding to adjacent wave crests, and the height and pitch rate (a2, b2) corresponding to wave troughs;

[0086] Determine a pitch rate slope Slope according to the height and pitch rate (a1, b1) corresponding to the adjacent wave crests and the height and pitch rate (a2, b2) corresponding to the wave troughs;

[0087] Slope=(b2-b1) / (a2-a1)

[0088] The comparison relationship between the absolute value corresponding to the pitch rate slope Slope and a given threshold value determines the dynamic behavior of the aircraft when approaching the ground.

[0089] The comparison relationship between the absolute value corresponding to the pitch rate slope Slope and a given threshold determines the dynamic behavior of the aircraft when approaching the ground, specifically including: Figure 2 As shown, if the absolute value corresponding to the pitch rate slope Slope is greater than a given threshold, it is determined that the dynamic behavior of the aircraft when approaching the ground is in a high slope change mode;

[0090] or,

[0091] Determining the dynamic behavior of the aircraft when approaching the ground according to the peaks and troughs of the pitch rate specifically includes:

[0092] Determine the height and pitch rate (a1, b1) corresponding to adjacent wave crests, and the height and pitch rate (a2, b2) corresponding to wave troughs;

[0093] Determine a pitch rate slope Slope according to the height and pitch rate (a2, b2) corresponding to the adjacent troughs and the height and pitch rate (a1, b1) corresponding to the peaks;

[0094] Slope=(b1-b2) / (a1-a2)

[0095] The comparison relationship between the absolute value corresponding to the pitch rate slope Slope and a given threshold value determines the dynamic behavior of the aircraft when approaching the ground.

[0096] The comparison relationship between the absolute value corresponding to the pitch rate slope Slope and a given threshold determines the dynamic behavior of the aircraft when approaching the ground, specifically including: Figure 3 As shown, if the absolute value corresponding to the pitch rate slope Slope is greater than a given threshold, it is determined that the dynamic behavior of the aircraft when approaching the ground is in a gradual slope change mode.

[0097] or,

[0098] Determining the dynamic behavior of the aircraft when approaching the ground according to the peaks and troughs of the pitch rate specifically includes:

[0099] determining at least one altitude interval range;

[0100] Set trough threshold and peak threshold;

[0101] According to whether there is a point in the pitch rate that satisfies a trough threshold and a peak threshold within the at least one altitude interval, the dynamic behavior of the aircraft when approaching the ground is determined according to the result.

[0102] For example, Figure 4 As shown, when an altitude interval is set, if the pitch rate has a point that satisfies the trough threshold and the peak threshold within the altitude interval, the dynamic behavior of the aircraft when approaching the ground is determined to be a specific altitude range mode according to the result.

[0103] like Figure 5 As shown, when two altitude intervals are set, if the pitch rate has a point that satisfies the trough threshold and the peak threshold in any one of the altitude intervals, the dynamic behavior of the aircraft when approaching the ground is determined to be a multi-level altitude change mode according to the result.

[0104] Alternatively, determining a dynamic behavior of the aircraft when approaching the ground based on the peaks and troughs of the pitch rate and the remaining data in the flight data;

[0105] Specifically, it includes: no peak or trough appears within the trough threshold and the peak threshold, and the touchdown distance value (VRTG) is in an appropriate range to determine the dynamic behavior of the aircraft when approaching the ground and the stability mode before and after touchdown.

[0106] If the absolute value corresponding to the pitch rate slope Slope is less than or equal to a given threshold range, and the touchdown attitude or VERF-touchdown speed is less than a set threshold, it is determined that the dynamic behavior of the aircraft when approaching the ground is in a touchdown micro-stability mode.

[0107] Among them, the high slope change mode has the rule that the slope between the peaks and troughs is relatively large, and the peak and trough thresholds and the slope threshold are all learnable parameters.

[0108] The gradual slope change mode has a rule that the slope from the peak to the first trough is small, and the peak threshold, trough threshold and slope threshold are all learnable parameters.

[0109] The specific altitude range mode has the following rules: a peak or a trough appears within 50-30 feet, and the peak and trough thresholds are both learnable parameters.

[0110] The multi-level height change mode has a rule that peaks or troughs appear within the ranges of 30-10 feet and 10-5 feet, and the peak and trough thresholds are both learnable parameters.

[0111] The stability mode before and after touchdown has the following rules: no peaks or troughs appear within 0-50 feet, and the touchdown distance value is in an appropriate range, and the peak and trough thresholds and the touchdown distance range are all learnable parameters.

[0112] The touchdown micro-stability mode has the following rules: no peaks or troughs appear, and the touchdown attitude is less than 2° or the touchdown speed is less than VREF by more than 5 knots. The peak and trough thresholds are learnable parameters.

[0113] The more modes that are triggered, the poorer the pilot's landing ability.

[0114] 1. The present invention adopts unique data processing technology and is optimized for the specific needs of the civil aviation field. It can accurately read, parse and analyze QAR data. Especially in the complex landing process, the system can efficiently capture key data such as pitch rate, touchdown distance, vertical load and speed, ensuring the high accuracy and reliability of the analysis results.

[0115] 2. The present invention combines pitch rate sequence change point detection with flight mode recognition. The system can accurately identify the pilot's specific behavior patterns during the landing phase, especially those non-standard operations or slight behavioral differences that may be overlooked in traditional methods.

[0116] 3. After the in-depth analysis results of the system are incorporated into the present invention, flight instructors and airlines can obtain clear and targeted feedback, and then adjust training strategies to ensure the continuous improvement of pilot skills.

[0117] 4. By utilizing the present invention, airlines can evaluate pilots' landing skills and risk behaviors more systematically and accurately, thereby conducting more targeted flight training and improving the effectiveness of training, ultimately achieving the goal of reducing the risk of flight accidents and improving overall flight safety.

[0118] In summary, the present invention proposes for the first time a pilot landing ability identification system based on the combination of change point detection and pattern recognition with data drive, which has broad application prospects and significant practical value.

[0119] The embodiment of the present invention also provides a device for identifying and analyzing a pilot's landing ability, the device comprising: a data acquisition unit, a pitch rate determination unit, and a behavior determination unit;

[0120] The data acquisition unit is used to acquire flight data before the aircraft lands;

[0121] The pitch rate determination unit is used to process the flight data by using a pitch rate sequence change point detection algorithm to obtain a peak and a trough of the pitch rate;

[0122] The behavior determination unit is used to determine the dynamic behavior of the aircraft when approaching the ground according to the peaks and troughs of the pitch rate.

[0123] The above technical solution is only one implementation mode of the present invention. For those skilled in the art, it is easy to make various types of improvements or modifications based on the principles disclosed in the present invention, and it is not limited to the technical solution described in the above specific embodiments of the present invention. Therefore, the above description is only preferred and does not have a restrictive meaning.

Claims

1. A method for identifying and analyzing a pilot's landing ability, characterized in that: The method comprises: Acquire flight data before the aircraft lands, the flight data including pre-landing data, time data, ground distance, touchdown distance data, vertical load data VRTG, speed data, pitch rate, radio altitude and time series data of attitude angle; The pitch rate in the flight data is processed by a pitch rate sequence change point detection algorithm to obtain the peak and trough of the pitch rate, specifically including: Select a window of size w and detect change points by sliding the window; Determine the statistical characteristics within the window, and for each time point t, determine the mean of the pitch rate of the two windows [tw,t] and [t,t+w] and Through the loss function Determine the loss value at the time point t; Determine whether a change point occurs at the time point t based on the comparison relationship between the loss value at the time point t and the threshold τ; If it is determined that a change point occurs at the time point t, the peak or trough of the pitch rate is determined; The dynamic behavior of the aircraft when approaching the ground is determined based on the peaks and troughs of the pitch rate, specifically including: Determine the height and pitch rate (a1, b1) corresponding to adjacent wave crests, and the height and pitch rate (a2, b2) corresponding to wave troughs; Determine the pitch rate slope Slope according to the height and pitch rate (a1, b1) corresponding to the adjacent wave crests and the height and pitch rate (a2, b2) corresponding to the wave troughs; The comparison relationship between the absolute value corresponding to the pitch rate slope Slope and a given threshold determines the dynamic behavior of the aircraft when approaching the ground; or, determining at least one altitude interval range; Set trough threshold and peak threshold; According to whether there is a point in the pitch rate that satisfies a trough threshold and a peak threshold within the at least one altitude interval, it is determined according to the result whether the dynamic behavior of the aircraft when approaching the ground is a specific altitude range mode or a multi-level altitude change mode.

2. The method for identifying and analyzing a pilot's landing ability according to claim 1, characterized in that: The obtaining of flight data before the aircraft lands specifically includes: Acquire flight data from Quick Access Recorder (QAR) data.

3. The method for identifying and analyzing a pilot's landing ability according to claim 1, characterized in that: The comparison relationship between the absolute value corresponding to the pitch rate slope Slope and a given threshold determines the dynamic behavior of the aircraft when approaching the ground, specifically including: If the absolute value corresponding to the pitch rate slope Slope is greater than a given threshold, it is determined that the dynamic behavior of the aircraft when approaching the ground is a high slope change mode or a gradual slope change mode.

4. The method for identifying and analyzing a pilot's landing ability according to claim 1, characterized in that: The method further includes: determining the dynamic behavior of the aircraft when approaching the ground according to the peaks and troughs of the pitch rate and the remaining data in the flight data; specifically including: No peaks or valleys appear within the valley threshold and peak threshold, and the distance to touchdown value (VRTG) is in the appropriate interval to determine the dynamic behavior of the aircraft when approaching the ground. The stability mode before and after touchdown; Alternatively, if the absolute value corresponding to the pitch rate slope Slope is less than or equal to a given threshold range, and the touchdown attitude or VERF-touchdown speed is less than a set threshold, it is determined that the dynamic behavior of the aircraft when approaching the ground is a touchdown micro-stability mode.

5. A device for identifying and analyzing a pilot's landing ability, characterized in that: The device comprises: a data acquisition unit, a pitch rate determination unit and a behavior determination unit; The data acquisition unit is used to acquire flight data before the aircraft lands, wherein the flight data includes time series data of pre-landing data, time data, ground distance, touchdown distance data, vertical load data VRTG, speed data, pitch rate, radio altitude and attitude angle; The pitch rate determination unit is used to process the pitch rate in the flight data by using a pitch rate sequence change point detection algorithm to obtain the peak and trough of the pitch rate, specifically including: Select a window of size w and detect change points by sliding the window; Determine the statistical characteristics within the window, and for each time point t, determine the mean of the pitch rate of the two windows [tw,t] and [t,t+w] and Through the loss function Determine the loss value at the time point t; Determine whether a change point occurs at the time point t based on the comparison relationship between the loss value at the time point t and the threshold τ; If it is determined that a change point occurs at the time point t, the peak or trough of the pitch rate is determined; The behavior determination unit is used to determine the dynamic behavior of the aircraft when approaching the ground according to the peaks and troughs of the pitch rate, specifically including: Determine the height and pitch rate (a1, b1) corresponding to adjacent wave crests, and the height and pitch rate (a2, b2) corresponding to wave troughs; Determine the pitch rate slope Slope according to the height and pitch rate (a1, b1) corresponding to the adjacent wave crests and the height and pitch rate (a2, b2) corresponding to the wave troughs; The comparison relationship between the absolute value corresponding to the pitch rate slope Slope and a given threshold determines the dynamic behavior of the aircraft when approaching the ground; or, determining at least one altitude interval range; Set trough threshold and peak threshold; According to whether there is a point in the pitch rate that satisfies a trough threshold and a peak threshold within the at least one altitude interval, it is determined according to the result that the dynamic behavior of the aircraft when approaching the ground is a specific altitude range mode or a multi-level altitude change mode.

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